Add a second 12V battery to a Prius

[@TerrellWSmith]

Corrections: At 7:35 in the video, it should say a ¼ inch bolt, not ⅜ inch. The ⅜ inch bolts go on the relay. At 11:32 I should have said 12 gauge wire, not 16 AWG.

[@Friendsshare]

Hey buddy you're a genius! This is amazing work here, you must be an engineer of some sort huh? Great job!

[@TerrellWSmith]

@Free Speech Thanks for your questions. Some of us enjoy making modifications, and my trips to the junkyard were a lot of fun and a good learning experience for me. :) Three points to note: 1) Since I run a refrigerator in the car off the second battery (see beginning of video), if I only had one battery and the refrigerator were to run it down, then the main battery is protected. 2) I use a solar panel (13:48), and because of the charging relay (19:10), the solar panel charges both batteries at the same time. They are also both charged when the engine is running. 3) Having a backup battery which is not anchored is dangerous if you have an accident. No one wants a battery flying through the air to hit them in the back of the head. :)

[@TerrellWSmith]

@Free Speech So far, the 2010 has been a great car for me. Be sure to check the oil from time to time, since it's new to you. Some users have experienced loss of oil. I have not. Check out priuschat.com for lots of helpful advice. Enjoy your new car!

[@TerrellWSmith]

@ddeeffe Good question. I don't know. I used my old Prius battery to avoid any issues. I don't know what the Prius charging system expects. But I do know that the second battery should be the same type (lead/acid) and not something different, because of the differences in charging algorithms. And my old Prius battery is also AGM (sealed), so it can sit inside the car. And it has a tiny vent hose, just in case, which I vent outside through the air vents.

[@user-eo4tb1dy7w]

Aaa

[@blueskies00]

Wow, ur one intelligent guy Why isn't there more subs?? Detailed, outlined, NO OBNOXIOUS MUSIC THOROUGHLY Explained Fantastic vid, 😊 thanks

[@TerrellWSmith]

Thanks for the kind words, Debbie.

[@nomadman1196]

I added a 2nd battery to my Prius V. I used the compartment on the left side, but I didn't bother to bolt it down, just covered it with the back matt. No Issues. To hook it to the other battery. I drilled through the other two posts and inserted a quarter inch bolt with a washer and nut. I just then bolted the positive to positive and grounded the negative to another bolt attached to the frame. I attached a 2000 watt pure sinewave inverter to the 2nd battery and use that to run a 12 volt fridge and a 700 watt microwave. Worked like a charm. 👍

[@TerrellWSmith]

Thanks for the report. Glad to hear it's working well for you. A couple of questions and thoughts: 1) Did you put a fuse on the positive side of the second battery? If not, I would highly recommend one. 2) You didn't anchor the second battery down? I hope you never have a crash. Having a battery hit you in the back of the head might be fatal. 3) Grounding through the frame is also how I did it, and that's the proper way. 4) Be careful how much power you draw using the 2kW inverter. The power comes primarily from your car's DC/DC inverter. The fuse on the Gen 3 12V battery is rated at 140A. I don't know what the rating is on the V. You're safe if you don't exceed 1kW. Enjoy!

[@nomadman1196]

@@TerrellWSmith You are right about needing to secure the battery, but I felt that with 4 battery cables attached that are secured with zip ties should hold it in place.

[@nomadman1196]

@ddeeffe Yes it needs to be the same battery that you already have. You have to go to Toyota to get one. 👍

[@sodade21]

you mean you did pair the 2 batteries directly with cables positive2positive etc without the fuses and parallels devices like in the video? you mention need to be the same battery..it can be 2 same batteries but not the original toyota ones?

[@nomadman1196]

@@sodade21 I connected the 2nd battery's negative to the frame. Both batteries were the same. The inverter was connected to the 2nd battery. I never pulled more than 700 watts on the inverter.

[@claytonchar9232]

Excellent video! Very detailed. I have a 2014 Prius and have started to thinking about RVing it in the 48 states. From watching several You Tube videos for the past 2 days it appears that the Prius is the perfect vehicle for solo RVing. Adding a second battery is a great idea. Eliminating a single point of failure is always a good idea.

[@jaweedDOTco]

Extremely detailed and informative. You have put a lot of effort into this video and that’s exactly what I needed. Thank you sir.

[@TerrellWSmith]

Thanks for the kind words, Jaweed. Glad it's helpful.

[@charissah9030]

Thank you for this information. I have two Optima Prius yellowtop deep cycle batteries, and have been considering a 2 battery set up for laptop use and camera charging on the road, as well as potentially a small fridge. This information is pretty clear and precise (especially for an electrical amateur like myself). I’ll probably watch this a few more times and then start the process. Thank you for this great walk through!

[@TerrellWSmith]

Hi Charissa, Thanks for the comment. Two thoughts: You might get a LiFePo4 battery power station, which can charge off your car or a solar panel to run the fridge. I recently added a Bluetti for this. kzbin.info/www/bejne/oKKsl5l7oNZ_q6c The Bluetti is plugged into my second battery, which gets charged from the car, and the refrigerator is plugged into the Bluetti. Your laptop and camera probably don't draw enough power to need a second battery. You can also watch my video regarding who might need a second battery kzbin.info/www/bejne/pZfVeqdpjNeaiJY

[@darthslackus499]

This is great info! I was looking to do something like this, but I'm terrible at DIY projects. You broke down the steps really well so I will attempt this soon.

[@TerrellWSmith]

Glad it was helpful!

[@BikeTall]

Very cool. I plan on getting a Prius to live & travel across the US for a bit. Looking to add more energy storage as I am a photographer and need to charge equipment. Your set up looks cool. I have seen some people attach flat solar panels to the roof so the battery is always charging during the day and you always have power at night.

[@gf2e]

I bet that a solar panel on the roof actually works out to be a net negative. The Prius is very efficient at converting gasoline into electricity. A solar panel will increase drag and reduce fuel efficiency.

[@shortygreyhannah]

What a great video! I don't have this style Prius, so I would need to see what kind of creative solution I can find, but the total knowledge gained here can be applied to my situation and is much appreciated!

[@TerrellWSmith]

Thanks for the kind words. Before doing anything, ask yourself whether you need it and whether a power station might be what you want. I have both and use both.

[@uradragon7823]

Well done and thanks. I have an 07 and you have given some good direction/instruction.

[@TerrellWSmith]

Thanks. The '07 might be slightly different. Check the fuse on the positive terminal of the 12V battery. On the 2010 it's 140A, but it may be less on the '07. Be sure to use a fuse less than whatever the battery uses, just to be on the safe side.

[@OTBkid]

Awesome, I hope I can do the same with my matrix. I run a diesel heater in it and this would give me peace of mind.

[@blueskies00]

Wow You are one smart guy. I get sooo mad at myself watching these videos, as I don't understand it and just feel plain Jane stupid. We all aren't gifted with intelligence. I'll show this fantastic video to someone who is gifted and pay them to do it. Thanks so much

[@TerrellWSmith]

Debbie, don't beat yourself up. You're smart to know what your limits are and when to ask for help. :) Be sure to watch my video on whether you need a second battery. kzbin.info/www/bejne/pZfVeqdpjNeaiJY

[@dezarydrak8241]

What I learned from you: 1.The 1000w inverter is the largest the 2012 Prius traction battery can use. 2. The Prius charging algorithm is not compatible with Lithium batteries (that was disappointing) . 3. I need to find a reliable salvage yard where the Prius taxis go to rest. 4. Find the most effective portable lightweight solar panels with the most wattage. 5. Need to review your instructional videos. Thank you

[@TerrellWSmith]

Thanks, Dezary. Just to be precise, the traction battery is able to provide more power, but the DC/DC inverter to the 12V battery cannot. 1000W is safe for that. The solar panels I use are lightweight, fold into a small package and produce 120W. AIMS Power. There is another way to add power if money is not an issue: Get a portable lithium power station. They cost around 1$ per watt, so a 500wh will run around $500. I didn't wish to spend that much, that's why I went with my setup.

[@TerrellWSmith]

Hi Dezary, there is a way to use a Lithium battery, or even better yet, a LiFePo4 battery. --> As part of a power station - because the power station can be plugged into the 12V output of the second battery (or primary, if you don't worry about draining the primary 12V battery, or if the power station has smart charging such that it cuts off when the voltage drops too low). The charging station has the circuitry charging algorithm to make sure the LiFePo4 (or Lithium) battery is correctly charged. I just recently added a Bluetti power station with a LiFePo4 battery to my set up, and will add a video about it.

[@DiAllinson]

I was just about to ask if the 2nd battery could be a LiFePO4 one. I'm completely clueless in this field but it looks like the answer is no is it?

[@DiAllinson]

I was going to do the inverter on the 12v prius battery then wondered how to run a cooler when I'm away from the car

[@jafinch78]

Neat detail, thanks for sharing! I wound up investing in two marine deep cycle batteries so I could use the 1500W inverter for 9A electric chainsaw and a hot plate. To save on battery requirements... last left off needed a soft or maybe a hard start capacitor either installed in or on the inverter or maybe in a box on the chainsaw side. For the 1000W hotplate, I found the lesser wattage demanding drink heater that can operate with the 100W directly from the 12V outlet. Haven't needed the chainsaw yet... so haven't done anything past using one battery... which used to be coffee grinder and Cuisinart... I guess the oscilloscope also for a test run. Great use of re-purposed material from the salvage yard and other resourceful sources and ideas! Thanks for sharing and the detail! Amazes me what can be found at the salvage yard... I stopped using junk and now say salvage. Even the prius's and other hybrids have neat say for example... pumps like from the inverter if you need or other parts that seem really awesome if you're into HV safely.

[@TerrellWSmith]

Thanks for the kind words. Please remember, the power mainly comes from the Prius DC/DC inverter, NOT the batteries. And to draw power safely from the Prius, 1000W is a safe limit. Having more batteries will give you a little more time before draining them, but don't expect to be able to run your electric chainsaw for long periods of time. At 9A X 120V that's about 1,080W (ignoring power loss from the inverter), which is close enough to the limit that it ought to work. I just wouldn't run that chainsaw for too long, in order to protect the Prius inverter. And as a reminder, make sure the Prius is turned ON. Yes, parts from a salvage yard are wonderful, and can be had fairly inexpensively. My experience is the salvage yard owner is happy to negotiate on price - a lot! I think they are happy to get rid of stuff.

[@jafinch78]

@@TerrellWSmith Yes, excellent point! I forgot to add that originally I designed for use in the pickup with an isolator and switch like you designed I think. 135A alternator and I really need to double check as I recall I designed for being able to switch as a backup starter in case the 12V vehicle battery died. Used an isolator and switch and fuse too with overrated gauge cable. I purchased some breakers also though haven't used or incorporated into the design plan yet. I never implemented in the Prius other than using the Prius to charge the batteries where I just used a car charger with 3A max charging through a 170W inverter from the 12V outlet. I never operated connected to the Prius as much as I wanted too like directly installing long term since was as needed use. I last installed at the farm building/station and haven't been able to be on the road the last few years. At the time I wasn't aware of the load limit and was under the impression 700W from an amateur radio operator who installed a 700W inverter. Recently, I think the same gentleman upgraded to 800W and has more details. I just commented on priuschat regarding (James Analytic) maybe last week seems. Now, I do plan to turn the truck into an RDF patrol rig and have been gathering equipment and tools to fabricate the design I want for the walk through and cap kind of like a Mike Basich design since I have a 2001 Dodge Ram 1500 and kept to do. I also want to fabricate a tail cargo area to lower drag that swings to the side to open on the truck and car one of these days. Thinking this winter will be a aluminum and steel welding and machine shop re-training season... then by spring maybe the foam and carbon fiber I hope. Technically, I'm wanting to make a alternator and engine welder with a CVT MG... and about to invest in the parts to do that next month as I almost did this month. Surprised no one has made an alternator for mains voltage with one yet. Seems a plasma cutter would be easy to design also since higher voltage... though whatever that "spec" RPM is for mains... seems win-win and cost effective.

[@jafinch78]

@@TerrellWSmith Thank you for kindly sharing! Also, I forgot to note... the 3 Phase rectifiers are really cost effective on eBay now days too. Just have to design cost effectively for the max current with some buffer of course overage for the solid state device. Amazed me how cost effective and like you noted... the parts from the salvage yard for the rest for the most part other than maybe outlets and switches at least for the generator/alternator. Now DC-DC conversion is a little more expensive at the higher voltage and current... unless maybe in parallel cheaper lower current rated devices/parts. That's what I've observed so far.

[@TerrellWSmith]

@@jafinch78 Wow, you've got some interesting projects going! PriusChat is a wonderful place to get information, that's where I learned about the 1000W limit, as well as other things. And as I understand it, the traction battery can provide 3k of power, but that's a bigger project than I'm willing to dive into. People have powered their homes with the Prius during a power outage. I've powered some things in our home during power outages with the Prius, but only the essentials.

[@jafinch78]

@@TerrellWSmith Yeah! That's awesome people are able to use their "portable generation stations" basically to traffic and power their lifestyle. Really awesome! Having a super hyper miling motor home is so neat and I like to also refer to as a portable power station too. Though what is kind of strange to me is the lack of anyone that I've found so far using the CVT Motor Generators (MG1 and/or MG2) whether inside the CVT case or in a custom fabricated case... as a alternator and/or generator. The alternator utility seems so easy and cost effective with machining or simple engineering skills. Where-as the generator system is more expensive and complex... especially if converting 3 phase AC to DC then inverting to AC. Hoping to inspire where I can... though a little hesitant since not only dangerous... I want to make maybe first or really not see a surge in CVT pricing once the cost effective highly reliable ways are identified. :-|)

[@TheChadWork2001]

People like you who know how to do this don't know what it's like to not be able to do this. Can i just pay you to do this on my car? Good work by the way.

[@TerrellWSmith]

Thanks. You should be able to find a shop that would be willing to help you with this. Make sure you get a price beforehand, so you're not surprised. :)

[@lindasue8719]

Really interesting and clearly explained! I feel like I could do it myself!

[@amywalker7515]

I"m 73 and did the inverter hookup from one of this other tutorials myself with the help of my son. As long as you attend to all the safety procedures, it's really not that hard to do.

[@darf26]

darf26 1 second ago Great video. Keep up the good work. Just one tip. When you connect 2 batteries together in parallel, you need to fuse the + at both ends as close as you can to the battery. If the + cable shorts to earth it will blow the single fuse that you have installed, but the short will still short circuit the unfused battery. The heavy cable that you have installed will probably carry 200 Amps upon short circuit. Unless you are very lucky the cable will heat up and likely burn your car to the ground. Very bad news if you are asleep at the time. Very small amount of work to remedy this. Again. Keep up the great work.

[@TerrellWSmith]

You are quite correct. That's why I used an original Prius positive battery connector, which has a built in fuse at the second battery's positive terminal. You can see it at 6:23 and 7:33. That positive connector has a built-in 140A fuse. Thanks for pointing out the importance of fusing both batteries as close as possible to the positive terminals for other users.

[@DCDura]

It's easier and safer to run the cables under the trim piece where the trunk latches. This is a shorter run to the primary battery and also there are several ground points. The existing wire loom can be used to zip tie the new cable.

[@TerrellWSmith]

Thanks for the comment, Dennis. Easier? I don't think so, because you need to remove the trim piece, tie up the cable, and replace the trim piece. Safer? Maybe slightly, depending on vibration and rubbing on the cable - but that's why it's fused at both ends. Shorter run? Probably slightly, but remember, I have the switch, so there needs to be a nice "home" for it. Ground points? None needed along the way, because both batteries are grounded on location.

[@JoelSJennings]

I have to ask, now that it’s been 3 years since you added a second 12 volt battery, have you had any issues or drawbacks? Has it harmed your hybrid battery or electrical system in any way? I still can’t find anyone to install a second battery for me in a 2019 Honda Accord Hybrid. The hybrid battery scared everyone away. Thanks.

[@TerrellWSmith]

Thanks for the question, Joel. I have not seen any issues or drawbacks or any harm. The hybrid system is able to keep both 12V batteries charged while driving, and when parked in a campsite, I connect my solar panels, and both batteries get charged then as well. I have now added a Li-ion power station, which is plugged into the second 12V battery so that it also charges while driving (or on solar), and my refrigerator is plugged into the Li-ion power station (EcoFlow DELTA Mini). The power station handles the difference in charging the Li-ion battery inside. To see whether you actually need a second 12V battery, you might have a look at my video here: kzbin.info/www/bejne/pZfVeqdpjNeaiJY

[@TerrellWSmith]

In the video, perhaps it's not clear that with this setup both batteries, the primary 12v as well as the second 12v battery, are parallel and charged while driving, as well as when parked (from solar). But when discharging, the second battery is independent, and will not drain the primary 12v battery.

[@BradyRay_333]

And that is what makes your setup especially nice.

[@jasonmartinez7667]

Does it only discharge when the car is not on?

[@TerrellWSmith]

@@jasonmartinez7667 , when the car in on, both batteries are being charged, as they are when solar is hooked up. When discharging with the car off, only the extra battery is discharging, protecting the other battery.

[@radiospank]

This is similar to adding a battery isolator and extra battery for car audio. So the second battery doesn’t drain the primary battery but they charge in parallel too.

[@TerrellWSmith]

@@radiospank - Exactly correct!

[@lawolfe2707]

Good video! I would love to see you do a video to help understand how you are using regular extension cords that are connected to your solar panels for charging. I think that is a great idea. I know a little about solar but not enough to rig regular extension cords to it.

[@TerrellWSmith]

Thanks. I simply wired a female plug to my solar panels (because that's where the power is coming from), then a male plug to my charge controller. Two warnings: 1) Only do this if you are the ONLY one connecting and using this setup. You do not want someone else thinking that this is a "normal" extension cord, and plugging it into a regular 120V outlet! 2) On the male plug, install a "dummy" female plug to protect the prongs of the male plug when not in use (remove this "cap" when hooking up your wires, then replace it when your done). This is because that male plug is wired to your solar controller, which is wired to your 12V battery. So you do NOT want a prong to accidentally touch the body of your car and cause a short to ground. One more warning: Only use THREE prong plugs and extension cords. That way you will always connect the extension cord(s) with the correct polarity. You do not want to use a two wire extension cord, because you might hook it up the wrong way.

[@lawolfe2707]

Thank you!@@TerrellWSmith

[@sleekitwan]

The venting thing you mention around @8:35 or so, I know the answer I think. In the vehicles I have had with a 12V battery in the engine compartment, there is never a vent pipe - they simply exhaust it right there, because it is considered sufficiently free space, open-air, that the battery directly can ‘vent to atmosphere’. However, in both the Volvo D5 Automatic I bought from 2003 vintage some time ago with its lovely 5-pot 20 valve engine, the battery was also under the trunk floor, like the Prius. The Volvo also had a vent pipe…and often people got batteries without a suitable vent hole for that, too! I therefor conclude, it’s either safety, or regulations. It’s always the case, that batteries of lead-acid type, give off gas, as they charge up. Indeed ‘charge until the battery is freely gassing’ is a common recommendation for lead-acid batteries. I fitted a really good spec AGM type of lead-acid, and it’s surprisingly really great, it belts out 14.5 Volts, where the previous dud was 12.4 or something. I know, because I fitted a lovely little $10 thing that plugs into the 12V cigar-lighter under the centre console open bit, and it is just always over to the clockwise except when one of the useful USB ports is charging my iphone! Then it cycles, it cannot show Voltage of battery when charging is all. Anyway, I proved conclusively that gassing while charging is a real thing by forgetting to pull out the tiny red ‘plasti plugs’ the manufacturer fits to the 12V battery…I forgot until 45 mins of charging took place…I prised it out finally and it shot out with a ‘pop’ and a hiss of gas. Hydrogen disulphide - stinks of rotten eggs. I suspect, the Prius is actually rather better at charging the 12V than people give it credit for, when everything is in full working order. Thus, that 12V battery, may well be ‘gassing freely’ when in situ in the trunk, and the hybrid car running well. That’s my info, take care all, thanks for the vid.

[@TerrellWSmith]

Thanks for the comments. Yes, indeed, lead-acid batteries vent. And the sealed ones, I understand, actually have little valves to allow them to vent if the pressure gets too great. There are very small batteries (like I have for my UPS) which are sealed, and do not look like they have a vent at all. But the 12V battery for the Prius has a vent, and it has a small hose to let it vent to the outside. For the built-in 12V battery, the vent hose goes through a hole in the floor. For my second 12V battery, I ran the vent hose out the little rubber vent of the car (which is to you can close the doors, and so the heater air flow has somewhere to go, and so -- it seems -- a mouse can find its way in!)

[@flyingcat2054]

Thanks for sharing! This helped with the install of a 2nd 12 volt battery big time! From there I am clueless how to use it to run things, and isolate it when I’m running a fridge and the car is off. I am a Prius camper and looking to up my game, either with a 2nd 12v or a power bank, but isn’t this the same as a power bank, and not as pricy? but I think I still need an inverter somewhere to power anything.

[@TerrellWSmith]

Thanks for the comment. At 9:14 I talk about installing the automatic charging relay, which allows both 12V batteries to be charged, and when the car is off, isolates the car's starting 12V battery from the frig. which runs off the second 12V battery. You simple add another aux port to that second 12V battery, fused at 10A.

[@sweetpea3472]

Awesome details. You have an electrical wiring mind & have provided the whole finished look & safe set-up. Very nice.

[@TerrellWSmith]

Thanks, Sweetpea, for the kind words.

[@safffff1000]

I'm new to Prius, but can't you just leave the Prius in ready and lock the doors with the key and have the car keep the battery topped off? And just put a 50-100 amp lithium battery where the Prius battery is since the Prius just needs 12 v for it's computers to start.

[@susie9893]

Yeah I got nearly half way thru this and being pretty puzzled b4 I realised this was an acid battery not lithium (I'd done a search about adding a lithium battery to your Prius and this was the only thing that came up). I just couldn't understand why it needed to be secured so solidly. But it's good know how to access that extra space - gotta be good for something

[@Bismarck666]

The Prius provides constant charge to the 12v. Doing that to a lithium will blow it up, you need a lithium specific battery Management system

[@sleekitwan]

Wow. Sorry to second-comment, but this is such a professional job - heck I was just gonna slap another one in, a smaller one, beside the first pukka Toyota one on that same side! I realised, there was an issue to do with the ‘lame duck’ of the two batteries, stealing energy from the good one. This is the thing everyone warns you against doing, fitting say one good AA battery in your remote control instead of replacing all of them, etc. It’s because the inefficient business of the good batteries charging the ‘lame duck’ member of their pack, is incredibly wasteful, and voltage drop also happens. In the EV world it’s called balancing as you will know. So yes, I realised there was needed some kind of diode ‘thing’ (technical term!) that would permit both batteries to be charged, yet NOT permit one to charge the other. So, in effect, while these two batteries ARE wired in parallel, they NEVER actually work like the parallel packs of AA batteries etc in consumer devices. They never ‘join together’ but they DO both put their effort into feeding the system that charges them. In other words - and I think you know best here - I think these batteries are actually isolated from each other completely except they both can supply power to the system they are connected to. Therefore, you can charge up one alone if you choose, without this charge, going over to the other one. The only way they are NOT isolated, is that they are BOTH CHARGING when the car is driving along? Or can do this? This is where some people diverge, saying that the car is not rated to charge the current supplying TWO batteries this size. I think this only matters if one or both is dying, and then the current will be large. But if they both are in rude health, neither actually takes much current, and the car takes no more current/power from two batteries than it would from one? Anyway, lastly, my idea was only to add in a second small, Li-ion battery. This is because immediately on buying my 2010 Prius 3rd gen, I experienced the dead battery I was not warned about by the vendor (!). The glitching drove me mad and much researching later on google, I realise ALL of the troubles - even the hybrid battery seemingly losing 4 bars overnight - was in fact a sign the 12V auxiliary battery was dead or dying. My idea was that if suitably isolated, then at least the 12V Li-ion once the car was ‘started’ would top-up the voltage and in fact permit the car to run possibly for quite a while, because if nothing goes wrong, it augments but never gets robbed of the 12V energy flowing into the car. That’s as long as one of those si-acr devices is used, I mean. Anyway, very nicely done, properly I’d say, thanks for the description and vid.

[@TerrellWSmith]

Thanks for the kind words. Just a few notes of warning: The Li-ion battery has a different charging algorithm than the lead-acid 12V battery. So if you substitute the original 12V battery with one of a different chemistry, you will likely overcharge it and likely kill it. The isolation switch I have does parallel the two 12V batteries anytime charging is happening (driving, solar charging, or trickle charging during cold winter days), but isolates the two whenever they are being drained (protecting the 12V battery which is necessary to start the car, such that my refrigerator won't leave me with a dead 12V battery on the car side). You are correct that two 12V batteries hooked together will work like two containers of water which are connected together, the lower one will pull water from the more full container until they both reach equal levels. So with the isolation switch installed, one 12V battery cannot "steal" charge from the other 12V battery while the car is sitting. If both 12V batteries are in poor shape, the car's charging system will be taxed more, charging them both. But that doesn't seem to be an issue with the Prius charging system. If it can deliver up to 1kW for running a microwave, it can simultaneously charge two 12V batteries.

[@mhughes8307]

The best video I’ve seen on adding a 2nd Prius battery. Clear information and well illustrated. Thanks, very helpful! Also, liked your penny pinching methods, after all, what’s a Prius about anyway? 😁👍

[@TerrellWSmith]

Thanks for the kind words. Yes, we Prius drivers like to save money. After all, we need to recover the extra we spent buying the car!

[@amywalker7515]

Imagine how much all those parts would have cost if he had gotten them all new.

[@saneauto]

Thank you for showing your great mods. I think Ill make something similar with solar and 4 Prius NiMH Modules. Ill video it too and put it in my Prius playlist.

[@gabaktech]

there is something called DC to DC charger for batteries, that will help you to have the battery in other place

[@terrellsmith2203]

GabakTech - What other place? The left rear corner is empty and a great place.

[@jasonmartinez7667]

Do you need the charger if your only going to use the battery when the car is on?

[@terrycoye3373]

@@jasonmartinez7667 If you are only going to use the battery when the car is on, you would not need a second battery at all, right? The car will automatically recharge the regular 12v battery as you draw down the power.

[@themoretruthfultruth]

The 12V Prius batteries are outrageously priced. I just had to replace mine and it was around $300. Takes a special battery because it is in the cabin.

[@TerrellWSmith]

Wow! I had to replace mine years ago, and it was over $200, but I don't remember what it cost. Yes, it's a sealed battery, has a vent pipe, and strange, small terminals.

[@clarkleyland1484]

well that was a good project but a lithium battery would give you more power an lighter an just have the solar charge it not tying it into the car system . You could just plug it into a cig socket while driving to your destinations charging it an then solar at the campsite. Just a thought.

[@christiankaiser8676]

We did this and it created all sorts of problems. The battery was a marine battery and had to be charged too often for our taste. The system charged the second battery on “ long drives “ which Prius drivers don’t generally take. One problem could’ve been that we had an 1100w inverter. 100 watts too many??? Now the ideal is to get a power station and dock it somewhere and be done. The ideal of a 500w inverter to the 12v Prius battery is being thought out currently as well. The problem is possibly upgrading appliances that may end up exceeding 500w

[@TerrellWSmith]

Thanks for the feedback, Christian. Was your second battery too small? Too old? For my project, I used my old Prius 12V battery, so it's the same size as the normal battery. I do take my Prius on long drives from time to time, like to Colorado for camping, to Texas to visit family, etc. But most of the time, it's driven around the city. And now during COVID, it's almost not driven at all! (I just ordered a battery tender.) The 1100W inverter shouldn't have been a problem unless you loaded it up past 1kW. And you did have the Prius in "Ready" mode, right? Otherwise you'll drain the 12V battery really, really fast. The power comes from the Prius DC/DC inverter. Were you hooking the inverter to the second battery? With the marine isolation switch, that would mean that while the inverter is pulling power, the switch might isolate the second battery, depending on the power flow, and instead of the second battery getting charged while the inverter is running, it just gets drained. I have my inverter hooked to the primary 12V Prius battery. The second battery runs low power drawing stuff, like the refrigerator. But even then, with no driving (or solar) to charge the second 12V battery, it will deplete after some days. My experience, three days if there's no charging. Make sure your inverter is hooked to the primary 12V battery. :)

[@DenaliDad]

Also, keep in mind the newer Priuses (like my 2016) has the battery up in the engine compartment, NOT in the back near the spare tire well. Running anything from MY battery requires breaching the firewall somewhere. Also, make sure anyone wanting to add a second battery knows to use a Toyota battery, not just any battery. In the Prius, they are proprietary and fulfill two functions...deep cycle and starter. Normal batteries don't do this because the Prius does not have a starter.

[@TerrellWSmith]

Yes, that's correct. Toyota moved the 12V battery to under the hood in the later Prius, which makes installing a second 12V battery (or an inverter) much more difficult. I do not recommend going through the firewall to install a second 12V battery, because there's not a very good place to locate it. And I also agree about the two 12V batteries be the same. Some people have suggested a different type of battery for the second one, but the charging algorithm for the Prius expects an AGM Toyota battery.

[@DenaliDad]

@@TerrellWSmith Another KZbinr posted his own setup; the two Prius batteries and a "regular" battery he added. As you said, the system does not recognize it--Toyota has proprietary batteries, not regular ones (oh, their magic!)--and the engine runs twice as long to charge that second one even though it really isn't "part" of the system. The only way I would breach the firewall is to add an inverter off the front battery...and I would have a pro do it. I saw one owner did it, but she had a *very* 'handy' husband; it's not something I want to do.

[@TerrellWSmith]

@@DenaliDad If the engine on that other YouTubber's Prius is running twice as long to charge that second battery, I bet it's also destroying the first (or second) one, especially if they are two different types of batteries. And may eventually damage the DC/DC inverter. The Prius 12V battery is an AGM battery, which has a different charging profile than a Lithium or LiFePO4 battery. To install my alarm system, I went through the firewall, but that was with a small cable, not a huge battery cable.

[@knitlover1]

@@TerrellWSmith Thanks; this discussion contains exactly what I needed to know because I was thinking how nice it would be use use a LiFePo4 battery instead -- no exhaust required, longer life, more capacity, etc. It's good to understand why that's not a good option. Thanks for a great video. I have a 2010 Prius and will be living in my RV in an area that lost power for a week last winter and doesn't have great sun exposure for solar. I first found PSC Camper Conversions' video for using a Prius as a generator and was thrilled that I wouldn't have to buy an emergency generator because I already have a nice, quiet one (the Prius). I was looking for a video with a more detailed explanation of the setup and was thrilled to find yours. Thankfully, one nephew is a Prius mechanic and the other has a junk yard. (-: I've now read on and saw your post about the Bluetti power station with a LiFePo4 battery, so I'll be watching for that video. Thanks!

[@TerrellWSmith]

@@knitlover1, thanks for the kind words. The reason for not adding a "raw" LiFePo4 battery is, as noted, that the Prius charging system isn't designed for it. BUT, if you add a LiFePo4 Power Station, such as the Bluetti (or other power stations), it has it's own internal charging system. So you can use the 12V port on your car to charge the LiFePo4 charging station, which should not be a problem at all (as long as you don't drain your 12V Prius battery). Having the second 12V battery in my Prius with the switch assures me I won't drain the main 12V battery charging the Bluetti Power Station. Actually, I THINK Power Stations are smart enough to turn off if the 12V source gets low, but I have not experimented on this. Sorry your area lost power for so long. We have used our Prius to power things in our home, such as the freezer, phones, computers, router, internet, and even a rice cooker and small microwave oven if necessary, but so far, it's been during shorter power outages (seven hours I think was the longest). Unfortunately, our refrigerator startup pulls too much power. When using the Prius for power, make sure it's not inside a closed garage. I use a flexible hose to vent exhaust outside. The exhaust pipe, because the Prius cycles on and off, doesn't get very hot. How nice to have family that can help you with the Prius and junk!

[@Urbaneism]

Can we get an update? Any issues with your DC-DC converter? I have a hybrid camry and been thinking about doing a two 12v battery set up. Thanks in adv!

[@TerrellWSmith]

Thanks for asking. No issues at all with the Prius DC/DC inverter. I think what's very important is to not exceed the DC/DC inverter's output. I have no idea what that might be for a Camry Hybrid; for the Prius 1kW is safe. Your challenge might be getting a heavy-duty wire through the firewall and locating a good "home" for the inverter, if your 12V battery is under the hood. Recently I added a Bluetti EB70 Power Station which has a LiFePo4 battery. The nice thing about this is that the charging of the LiFePo4 battery inside the Bluetti is controlled by the Power Station. I plug the Power Station into a 12V socket coming from my second 12V battery. This way all three batteries are being charged while driving, or when my solar panels are plugged in. My refrigerator is then plugged into the Bluetti, and my estimate is that it will power the refrigerator for three days and nights even if I'm not driving and the skies are cloudy or overcast and I don't get much from solar.

[@Urbaneism]

@@TerrellWSmith Man thanks for the response! I have a car audio system approx 900 watts max. My problem is parasitic drain when the car is off. Im thinking a second 12v with an isolater should do the trick. I know the Prius has a 100 amp fuse to protect the DC DC converter which charges the 12v battery. Im sure the camry has the same fuse, just not sure what the amp rating is. So, worse case scenario, if I over do it I just blow and replace a fuse?

[@TerrellWSmith]

@@Urbaneism, that's a big boom car? :) Parasitic drain is a problem, yes. You just drive around the neighborhood more! Kidding aside, have you considered installing a switch that cuts power to your big audio system? The Gen 2 Prius might have a 100A fuse, the Gen 3 has a 140A fuse. You can check the amp rating for your Camry. If the battery is similar to what they install in the Prius, the red cap on the positive 12V terminal has a built in fuse. You do NOT want to blow it. It's not a fuse you can easily replace with fuses from a store. It's a propriety Toyota fuse built into that red cap, and I would guess, expensive. Right now, you're running your 900W audio system, right? How is it connected? Directly to the battery? Is it fused? Where is that fuse? Under the hood? Inside? If inside, what if you added a switch? That would likely be much easier than going through the firewall. Did you do the install? Or have it installed? If a shop installed it, you might ask them about the drain when your system and car are off. I don't think that should be happening if they did a good install. Because you could go somewhere for a while only to come home to a dead battery.

[@Urbaneism]

@@TerrellWSmith Noted! Thanks 💯 It was professionally installed. You're right, I'll asked if they connected the remote wire appropriately to ensure the amps are truly off when the car is. I'll have them troubleshoot that parasitic source. Yes, directly connected to the battery. Yes, the amps themselves are fused and so is the power cable from the battery to the amps. (not sure at what amperage, id have to check). I'm not sure what a "Switch" is or how it compares to an isolater between two parallel batteries, but im about to research. Now, is this built on fuse with the red cap on the battery the fuse that protects the DC DC Converter? I assume I can just inspect it to see the rating. I called the dealer and even the manufacturing plant (so they say) and they act like it's a big secret yet its public knowledge for the Prius.

[@TerrellWSmith]

​@@Urbaneism, yes, you need to figure out that parasitic drain, otherwise having a second battery does you no good, it will get drained as well. By "Switch," I just mean a simple on/off switch. Yes, if your 12V battery has the built in fuse, it protects the DC/DC inverter. Yes, you can inspect the thing to see what the rating is, IF you have the built in fuse on the red cap. If you watch my video at 13:12 you can see the red 12V battery cap, which is easily lifted up when you squeeze the little tab. Under it you will see that there's a white cable coming into the battery. That's from the DC/DC inverter. And there's a built in fuse as part of the way that cable is attached to the positive side of the 12V battery. At least, that's what it looks like on the PRIUS. I have no idea what things look like on your Camry. When you wrote that you asked the dealer as well as the manufacturing plant and they wouldn't tell you, I laughed. They don't like anyone to add aftermarket stuff to their cars, because they don't want to fix something which got messed up by an aftermarket install. My daughter wanted to have a CD player installed in her Toyota, because they don't include them since 2018, but the dealer told her it would void the warranty for someone to mess with the wiring. (I've installed all sorts of stuff in my Prius, and when I tell the dealer, they want to see it, because they are impressed.)

[@look11223]

Subscribed because I like to support your sharing Spirit

[@TerrellWSmith]

Thanks, Leung, for the kind words. I like to share, and am thankful for His Spirit. :)

[@lawrencelile]

Using a regular 120v extension cord for DC is really dangerous. Someone not familiar with the setup could inadvertently blow it up. I would never do this. Electricians call these "suicide cords". Good luck and stay safe.

[@TerrellWSmith]

Thanks for your comment and concern, Lawrence. In this case, though, it’s not dangerous for a couple of reasons. I use it when I’m in a remote area - where there is no 120v outlet to plug into. Plus, when I use it, I’m the only one using it. (If I were with others, especially kids, that might be another thing. But again, there’s no 120v outlets around in the boonies.) And I don’t believe it’s what electricians call a suIcide cord. That’s a cord with a male plug on both ends, which, when plugged in, is very dangerous indeed.

[@markb8954]

@@TerrellWSmith. Agree. Suicide cord = two male ends on a cord when people try to tie in their generator into their house.

[@erinsjourney315]

😱 This is bloody brilliant!

[@jakeliujakeliu]

This is great please make more video!

[@TerrellWSmith]

Thanks for the kind words, Jake. See: kzbin.infovideos

[@goodgogo100]

great good info,thanks,I'll try someday

[@LordPowerbang]

Thanks for making this.

[@radiospank]

The comments are hilarious, so many people hating on a very thought out and practical second battery install. Many just don’t understand enough about electrical and start saying dumb comments and or trying to say the single battery is adequate. Lol

[@TerrellWSmith]

Thanks, Radiospank, for the nice words. Some people don't need a second battery. But for camping and my refrigerator, it protects my primary 12V battery.

[@DCDura]

Also safer to run the LED wire under the trim pieces at the door sills. You don't want to damage the existing wires poking and pulling it through with a coat hanger. These pop off very easily.

[@TerrellWSmith]

The LED wire is run under the door trim. Thanks for the clarification - the coat hanger was not used to poke the wire through under the door trim - gentle poking with your fingers does the trick, without removing the trim. The only times I used a coat hanger "fish line" was to go from the back trunk area to the back seat area, then again up front to pull the wire up into the center console. I did these carefully and gently.

[@triple_gem_shining]

Indefinitely wanna do this!

[@yakinkate7946]

Awesome teaching video. Thank you.

[@TerrellWSmith]

Thanks for watching, and the kind words.

[@JoelSJennings]

Did you leave your original SLA battery in place when you added the AGM? Every shop in my area has refused to replace my original 2019 Honda Accord hybrid battery with an AGM and then adding a second battery (also AGM) in the trunk saying the electronics of a hybrid are way too sensitive to handle any slight fluctuation in charge. I believe I am correct, and I have tried to explain the original 12 volt battery is only for starting and everything is then handled by the hybrid battery which nothing should touch. Any advice? Thanks.

[@TerrellWSmith]

Thanks for the question, Joel. Yes, I did leave the original 12V battery (AGM I'm pretty sure, because in the older Generation 2 & 3 Prius, it's inside the car, not under the hood. It is vented by a small tube to the outside.), and added the exact same 12V as my second one (I bought a new 12V for my "main" car battery, and used the "old" 12V for my second 12V battery) -- precisely because I was unsure what the DC/DC inverter might "think" when it encountered a different battery. The DC/DC inverter reduces the traction battery's Voltage to 12V to power all the electrical accessories. In Ready Mode (the car is "on"), the 12V battery just serves as a "ballast" to the 12V system to smooth out the 12V power a bit, and provide power (or a place to sink power) when there is a sudden load change. In general, I would think an

[@JoelSJennings]

@@TerrellWSmith Thank you for your quick reply. I guess I’m going to be stuck using an unconnected AGM in the trunk and charging it frequently.

[@TerrellWSmith]

@@JoelSJennings Be careful to not discharge it too far, it can damage the battery. If you're not traveling for many days at a time, one thing you could do is charge it with a "smart charger" when you have available 120V. Due to COVID and not driving my car for long periods of time, I got one from Costco which will charge the battery and shut off (thus a "smart" charger): www.costco.com/battery-tender-4amp-smart-battery-charger-and-maintainer.product.100519712.html

[@JoelSJennings]

@@TerrellWSmith If I may ask one more stupid question. Is there any difference between this set up and using a standard dual battery isolator kit? From what I’ve read, and from what little of that I’ve understood, they appear to be accomplishing the same thing. Just FYI, I received my 2 XS Power AGM batteries, smart charger and related accessories today. I’m still waiting on the cabling and the solar panel. Thanks for all your help!!

[@TerrellWSmith]

@@JoelSJennings No question is stupid, but sometimes answers are. :) What little I know, both will do the same thing for you. I think a dual battery isolator kit is more expensive, and some older ones use diodes, but I believe new ones are solid state with no voltage drop.

[@digimikek]

great work! thank you for your efforts and video

[@TerrellWSmith]

Thanks for the kind words.

[@martineavila5708]

very informative video. Thanks.

[@TerrellWSmith]

Thanks for the kind words.

[@JoelSJennings]

Would you consider doing a similar install in a 2019 Honda Accord Hybrid? If so, what part of the US are you located in? Thanks.

[@TerrellWSmith]

Thanks for the question, Joel. Sorry, no, I don't do installs for others. But you might find someone in your neighborhood who would do it for you.

[@waynefreeman595]

I'm looking at installing an inverter in my 2014 PriusV. I watched your video, and was surprised you didn't mention an inverter. Do you have any thoughts on whether your setup is actually better than an inverter? Did you ever get an inverter for yourself? Thanks for the video...

[@TerrellWSmith]

Here's my video on installing the inverter kzbin.info/www/bejne/g6uvhXWvq6-KbcUsi=XdX50HzoO_ayslzQ in my Prius. Adding a second 12V battery is not the same as adding an inverter, as you suspected.

[@peter2182]

Could the second 12V battery be a 100Ah mini LifePo4 battery instead of AGM battery?

[@TerrellWSmith]

Yes and no. If you use a different battery chemistry, the Prius doesn't know it, and might not charge it properly, and especially overcharge it, ruining it. But you can use a LiFePO4 battery so long it's in a small power station, like an EcoFlow, BLUETTI, or similar, because they have the correct charging algorithm built in. Just plug this into your 12V power port to keep it charged.

[@peter2182]

As an alternative solution to the power station option, how about a RENOGY or VICTRON DC-to-DC Charger for Lithium LiFePO4 which can prevent any damage to both the car alternator and the battery while charging at a much higher current such as 20A instead of 10A?

[@TerrellWSmith]

Good question,@@peter2182 . Unfortunately, I'm not familiar with those. The key factor is the charging algorithm, which needs to be correct for a LiFePO4 battery. If you find out, feel free to post your results here.

[@ntulsian]

You mentioned getting power station that will manage rhe Li battery inside. All lithium batteries have a BMS which controls rheir charging and diacharging, so wouldnt that be enoigh toamage an independent/non-power-station Li battery?

[@TerrellWSmith]

Thanks for the comment. Newer 12V lithium batteries should have a Power Management System (BMS) built in. If not, the Prius charging system assumes a lead-acid 12V battery, and will overcharge a plain lithium battery. A power station has its own built-in power management system, so whether it has a LiFePO or something else, it shouldn't matter, it can be charged off the car's 12V outlet, solar, or whatever. That's why I mention getting a power station. My "Add a second 12V battery to a Prius" is based on saving money. I had a second 12V Prius battery available, and power stations were expensive. A lot has changed in battery technology in the last 4 years, plus power stations are much less expensive now. And a good 12V lithium battery ought to have an internal BMS now, as you say. :)

[@dgordon6378]

I know this is for small appliances or devices, but is there any change in mpgs since you did this?

[@TerrellWSmith]

Thanks for the good question. Obviously, there's no free lunch, and as they say, YMMV (your mileage may vary). But I have not observed any measurable change since adding this. I've tracked my mileage since buying the car. Things that probably have more of an effect are tires, weather (cold drops the mpg a lot in an hybrid), driving style, speed, terrain, how much junk you haul around, etc. I've averaged 45 mpg over the total life of the car, with a high of 62 mpg and low of 33 mpg.

[@SaveAPennyBustANut]

Do you get more mpg or power this way? Install a beefier sound system? What else can you do by installing a second 12v,?

[@TerrellWSmith]

No, no more mpg nor power this way. That would be magic. :) My main goal was that my refrigerator would not slowly drain the main 12V battery while camping on cloudy and rainy days when I wasn't getting enough solar to keep my main 12V battery up. Another way to do this, of course, is to bring along a "power station" and plug it into a 12V aux port, and run the refrigerator off of the power station. That's what I do now, in addition to having the second 12V battery. If you install a beefier sound system for your wild beach parties, yes, this would allow you to drive away after draining your second 12V battery -- but during your party, you probably would have your car on, to provide 1000 watts to your speakers. (Which your friend brought in his pickup truck.) ;)

[@HarryOttele]

I would like to see a Convertion of a Prius to a Home Stand by Generator. Locking up the trans to make both motors into generators.

[@TerrellWSmith]

See kzbin.info/www/bejne/g6uvhXWvq6-KbcUsi=rPj8WFR89GI5-BiN where I share about adding a 1kW inverter to the Prius. It's not "standby," you have to set it up and turn it on. And you don't "lock up the trans to make both motors into generators." You simply leave the Prius in "ON." The gasoline motor will auto start whenever it's needed. And it's not practical to have the electric motor running to generate power, since it's using even more power to run. Again, you don't need to be concerned about it, because the Prius does it all for you. You can run extension cords from the inverter to the appliances you need to run, being careful to not exceed the 1kW of power from the inverter, or it will shut itself off. After going with extension cords for a while, I installed a transfer switch, so now it's pretty much "plug and play."

[@yv6eda]

Great tutorial, thanks!

[@roydredge1273]

in part of your video you mention putting a fuse in the negative cable thats usually a big no no unless un special circumstances

[@TerrellWSmith]

The main fuse goes on the POSITIVE side of the battery. That little 1A fuse to ground on the relay is per instructions (if I remember correctly), just so the relay is completely protected. Probably not necessary.

[@roydredge1273]

11:12 why

[@carlossaavedra6109]

Thanks for the excellent vid! R u an engineer? Guessing yes as this is very thorough.

[@TerrellWSmith]

Thanks for the kind words, Carlos. I'm not an engineer, but I did study Physics at Cal. When I was growing up as a young boy I started tinkering with electronics, subscribed to a monthly electronics build-it kit, built radios (from a simple crystal radio which needed no batteries, to a short-wave radio), and enjoy thinking of how things work.

[@carlossaavedra6109]

@@TerrellWSmith Thought you had a STEM background. Thanks again for the vid. Will be using it as a launch point for my own Prius house battery.

[@gotaigo]

Quite involved but probably worth it

[@TerrellWSmith]

Thanks for the comment. It is worth it for some, but not for others. I've made a video here kzbin.info/www/bejne/pZfVeqdpjNeaiJY to help people decide whether they need a second 12V battery or not, based on their power needs.

[@amywalker7515]

Thanks for yet another great video. Am wondering what you can run with this battery as far as number of watts and for how long? Why can't you merely have the main battery and starter battery recharge the additional battery when you drive? Or if you're camping, couldn't you merely leave the car on in "ready" and it will get recharged if you're drawing continuously from it? With 2 batteries, could you draw more than 1000 watts at a time if you had the correct inverter?

[@TerrellWSmith]

Hi Amy, With the relay, the second battery and the main 12V battery ARE charged when I drive, or when I connect the solar panels. The relay disconnects the two 12V batteries when they are not being charged, so if I don't drive for a time, my "stuff" (like the refrigerator) doesn't drain the main 12V battery. While camping, yes, if the car in in Ready, then both batteries are being charged. And the gas engine cycles on and off as needed. Which I did once in a campground on a hot night to allow the fan to run. But I got complaints, even though the engine is very quiet. Plus the car rocks slightly when the gas engine starts up, and it would wake me up. With two batteries in this set up, no, you cannot draw more than 1000 watts at the same time, because the main power comes not from the 12V batteries (which are very small), but from the car's DC/DC inverter. If you really need to draw more than 1kW, I suggest adding a Power Station which delivers the wattage you need. The power station can be plugged into your second 12V battery so it recharges while you drive (or from solar). You just need to keep an eye on the power station so you don't totally drain that battery. I have a small 700W power station plugged into my second 12V battery now, so I have enough power to run my refrigerator for about three days when there's not enough solar. As far as your first question about number of watts and for how long, that depends on the condition of your second 12V battery. Mine is pretty old (it was my main 12V battery earlier.)

[@amywalker7515]

@@TerrellWSmith Thanks for the detailed reply. So many ways to set things up. A large power bank would be great but wouldn't it take up a lot of room?

[@TerrellWSmith]

@@amywalker7515 Yes, a Power Station can be heavy and take up lots of room. But they come in all sizes. My Bluetti EB70 with a LiFePO4 battery gives 700W, has 716Wh, weights 21 lbs, and is (LxWxD) 12.6 x 8.5 x 8.7 in (32 x 21.6 x 22.1cm). I fit it in the back on the left behind the second seat. The newer version EB70S gives 800W. An EcoFlow Delta Mini with a Li battery gives 1400W, has 882 Wh, weighs 23.6 lbs, and is 14.9 × 7.2 × 9.4 in (37.8 ×18.4 × 24 cm), slightly larger. The Li battery (lasts only 800 cycles to 80%) doesn't take a charge as many times as the newer LiFePO4 (2500 cycles to 80%) batteries. I do not own an EcoFlow, but I've thought about it. One thing to note is even though something may give you a lot of wattage, the Wh (Watt hours) are also important, because that tells you the capacity. So you may be able to run a microwave but it will suck a lot of power out of the power station, then you spend hours re-charging the power station. That's why using the Prius built in DC/DC inverter is so nice. You can run it all day and it provides power (well, until you run out of gas).

[@C4M3120N]

TerrellWSmith Thank you very much for making and sharing this video. I have a couple of questions that I hope you wouldn't mind answering before I do this to my own Prius. Is the parallel indicator light and wire that you ran from the relay towards the dash absolutely necessary? To me it seems like an unnecessary step if the rest of the system was installed correctly. Am I not understanding the importance of it? I'm asking because I would like to avoid that step if possible. My second question is in regards to installing a power inverter in my Prius. I have watched your separate video on that as well. However that modification to your Prius was done long before this second battery modification. I would much rather run my inverter off of the second battery setup. So I would never have to worry about accidentally draining or killing the starting battery from inverter use or failure. Do you think that would be a good or bad idea? I would like to add a second battery with the dual charging relay you used. I would like to run an 1000w-1500w inverter off of that second battery. I would also like the ability to charge that second battery with supplemental solar power when camping. Any advice or suggestions would be deeply appreciated. You literally have something very similar to what I want already installed and field tested. Thank you again! Stay safe and have fun!

[@TerrellWSmith]

Thanks for your kind words and questions. Correct, the light that indicates it's in parallel is only optional, and not necessary. Regarding the inverter, it MUST be run only while the car is in ON mode, otherwise you will very quickly drain your 12V battery. The Prius provides the power to run the inverter, not the 12V battery. Assuming your second battery is being supplied by the Prius (since you wouldn't have the indicator light), you'd be OK. Personally, I would hook your inverter to the original 12V battery as in the other video. Do NOT run a 1500W inverter off this system, 1000W is the most it can handle safely. Yes, you can charge the second battery with solar, I do that. I have a foldable solar panel I put on the windshield while parked (or on the ground, or the roof - wherever I get the most sun). Make sure you use a good solar controller. The power from the solar on the second battery will charge BOTH 12V batteries due to the switch which parallels the batteries. You can listen and hear it click over when the sun provides enough solar power. You can also observe the voltage change when it switches to charging both batteries. Solar will NOT make enough power to run the inverter. Only the car will. May you enjoy the modifications! I have a lot of fun showing people my setup while camping. "No, the solar doesn't charge my car, it charges my refrigerator," I say. "What?! You have a refrigerator in there?!" Yep. My next video will be on the toilet. :)

[@feredonferedon3998]

Thank you very good video so can I use second battery for 1500w power inverter and I know I’m not turning the engine off if I use the inverter 👍

[@TerrellWSmith]

Feredon, thanks, I'm glad it's helpful. You can safely use 1kW, not 1500W. The power comes from the Prius DC/DC inverter, and you don't want to damage it by drawing too much power. You are correct about not turning the engine off while drawing power. Just keep it under 1kW to be safe.

[@jorgemora7190]

Wow very good video bcse l never see it before but today,learned a lot think from you Mr good guy also the prices too hahahaha God blesss you

[@TerrellWSmith]

Thanks for your comment, glad you learned some new things.

[@williamingalls7473]

Will the second battery help start the car or is that what the relay prevents?

[@TerrellWSmith]

Thanks for the question, William. The purpose of the relay is to protect the main 12V battery from getting discharged by something, like a refrigerator, so that it CAN start the car. If, for some strange reason you were to totally discharge the main 12V battery (say, you left the dome lights on for a very long time, which do not auto shut off), you could use the second battery (assuming you have not totally drained it with your refrigerator, etc.) to jump the main 12V battery. The second 12V battery is to run whatever is plugged into it, the relay protects the main 12V battery from getting discharged so you can start the car.

[@williamingalls7473]

@@TerrellWSmith Awesome thank you. For some reason my old 2005 12v needed to be replaced a lot. Now I'm in another 2005 where I've only had to jump it once in reallllly cold weather. I think it was a short somewhere but it was easier to trickle charge than diagnose.

[@calvinshum8019]

Hi thank you very much for your video. I just bought 120ah deep cycle battery which is much bigger than my 2004 gen2 prius starter battery. Have I bought the wrong 2nd battery and should I exchange it for a smaller one same as the started battery? I have also bought the smart isolator to isolate the starter battery and 2nd battery.

[@TerrellWSmith]

Hi Calvin, the most important thing is that your second 12V battery is sealed lead/acid. 1) Sealed, so that it doesn't spill anything into the back of the car. There should be a vent on it, which you can vent through the small rubber flaps back there. Batteries generate small amounts of hydrogen gas, which is why it should to be vented. If you look closely at the Prius 12V battery, there is a small tube coming from the battery and going out through a small hole to the outside. 2) Lead/acid, because the charging algorithm of the car expects that. If your second 12V battery is a different chemistry, your charging system might damage the battery, even kill it. 3) As far as size, I don't know enough about the charging system to know whether it will handle a larger battery. Maybe or maybe not.

[@calvinshum8019]

@@TerrellWSmith thank you so so much for your answer. I just checked my 2nd battery. It is sealed and acid. Can I put a dc2dc charger to protect my 2nd battery? However prius doesn't have an alternator, do you know it will work? My set-up is dual battery system plus a 1500w inverter. Thank you for getting back to me. I really appreciate it.

[@TerrellWSmith]

@@calvinshum8019 Hi Calvin, sealed is good, and acid (sometimes called flooded) is good. Does it have a tiny vent? It might not. And if it does, you might not see it. The Prius 12V battery has a little hose attached to the battery to vent outside. Not sure what you're thinking regarding a dc2dc charger. The Prius dc/dc inverter will supply enough to power 1000W, not 1500W. Check what size the fuse is on the positive side (built into the positive terminal of your 12V Prius battery). On Gen 3, it's 140A. On your Gen 2, I think the fuse might be less. Make sure you fuse your second battery to less than whatever your Prius 12V battery's fuse is, to protect your system. I fused mine at 100A. You can run your 1.5kW inverter if you're careful to not go over 1kW. Note that the power is not really coming from your 12V battery, but from the Prius dc/dc inverter, which feeds to the 12V battery. So having a second 12V battery which is larger than the Prius 12V battery doesn't mean you can pull more power. (Well, technically you can, but only for a very short time, and it could damage your system.)

[@calvinshum8019]

Hi thank you for your reply. I really appreciate your effort. I am very new to this technical thing. Your help has helped me heaps. I just checked the battery. It is 50A, a very small one. I actually want longer power for my fridge, should I add 2 batteries or solar instead? I am going to refund my new battery for the same battery as Prius (my new battery is not opened yet and thank you for helping me as I may have opened the box without your message).

[@TerrellWSmith]

@@calvinshum8019 Hi Calvin, just want to make sure you're looking at the right thing. Not the battery you bought, but the 12V battery in your Prius. On the positive terminal, there is a red battery cover (2:20 in the video). If you remove this cover, you should be able to see a fuse (6:22 in the video). On the Gen 3, you can see it's marked 140A. I would think that on your Gen 2, it might be 100A, not as small as 50A, but I could be wrong. Adding two batteries doesn't help, because as I mentioned in my post earlier, the power is not coming from your 12V battery, it's coming from the car's dc/dc inverter. Solar will help, but only as long as the sun is shining, so it doesn't help much on cloudy or rainy days, nor at night. I have solar to charge things back up during the day. You need to know how much power your fridge needs. Is it a compressor fridge? Or one with a chip? A chip fridge draws more power than a compressor fridge. Perhaps you can use a portable power station, such as the Bluetti EB70S or the Ecoflow DeltaMini. You can plug one of these into your 12V aux outlet in the car, and it will be charged while you drive. Or you can use solar to charge it. One of these portable power stations will power your fridge for 2-3 days, depending on the fridge's power needs. Downside of a portable power station is they are expensive. With the second 12V battery in your Prius, as I have, the second battery charges as you drive (that's the relay at 9:16 in the video), or from solar, and your primary 12V Prius battery is protected from being drained by your fridge. So after a few days of not driving you can still start the car! If you get as your second battery another 12V Prius battery, you won't need to be concerned about the car's charging system, because it's already designed for that battery. Downside is that Toyota charges a lot for one. Once you know what that fuse size is on your Prius 12V battery, you will have an idea of what you can draw for power. The Gen3 fuse is 140A x 12V = 1680W, which is far too much. I use a 100A fuse x 12V = 1200W, with a 1kW inverter to stay on the safe side. If your 12V battery really is fused at 50A, the very most you can draw is 50A x 12V = 600W, not 1500W. And at 600W, you'll blow the fuse. (Calculations are in an ideal world, which the car is not, because there are other factors.) But just so you get an idea of why you cannot pull 1500W. Hope this is helpful.

[@RobertGolden1952]

why not use a manual switch to choose which battery is operational?

[@TerrellWSmith]

That works for someone who ALWAYS remembers. But most of us forget sometimes. :) The automatic switch works without having to remember to turn it off (to isolate) when discharging, and on, every time you're charging (driving, solar, charger).

[@KarmicPatina]

So great! Thanks buddy.

[@anupmankar8676]

did you consider a DC to DC charger rather than an automatic charging relay? If you did, could you explain why you went with the relay? apologies if this is obvious, i'm new to this stuff :)

[@rspaulding]

Instead of charging it with solar, can you use the hybrid battery to charge it?

[@TerrellWSmith]

Thanks for asking. The way it's set up, the second battery can be charged with solar, or with having the car turned to ON (which charges it from the Prius charging system, same as when driving). It also gets charged if you connect a charger, such as a trickle charger.

[@ricecowboy]

Great video! I would love to see a diagram of your setup which would be immensely helpful. From what I can gather, it looks like you’ll be drawing from the starter battery (instead of house battery) to your 1kw inverter, correct?

[@terrellsmith2203]

Thanks! Yes, the 1kw inverter draws from the regular Prius 12v (starter) battery, because a lot of the power is actually coming from the Prius inverter. So the car must be turned on. Otherwise the (starter) battery would very rapidly be drained. I plug my refrigerator into the second 12v battery, since it's draw is much less. Both batteries get charged when the power input from my solar panels, or from driving (or parking with the car turned on) exceeds the power draw, due to the added switch. So far, it's worked without any issues.

[@ricecowboy]

Terrell Smith Makes sense. There’s another KZbin channel (Boondocking Bears) who drew inspiration from your video, but rather than using an Anderson connection, he installed his inverter directly to his starter battery and installed a remote power switch for his inverter. Seems like a great idea. Cheers. Hope to see more videos from you.

[@woody3307]

Terrell, I read all your findings and comments below with great interest. I too have been down similar path and ended up with Bluetti 1kw, then Jackery 500. Jackery only charges at 85 watts, and the Bluetti charge was too high watt for the cig lighter. Hard to get those things charged up with solar or even with car without a lot of pains and time so the simplicity of the second battery has a lot of pros. For years I ran my Prius using a 35 amp hour smaller AGM battery, and I have several of them still even though I do my best to ruin them leaving that light on...or something. But I was going to use the smaller AGM with my recent full size replacement as the second battery. They should both have the same charge voltage parameters essentially. Do you think the size difference between the large and the medium size would cause issues? I did note that my trickle charge never seems to go green with smaller battery hooked up, but the current is really low. I also have a leftover negative disconnect and was just thinking of using that on the second battery and manually doing the switch on and off. Would I forget?? Haha..no doubt, but it wouldn't affect the main 12 v I think. And lastly do you still have the trusty Prius?? Thanks for all the great info. PS, to save your readers emotional upset please delete the comments from complaining negative people as it only confuses and upsets us. I know you are a gentleman and trying to be fair and patient etc, but people who use harsh language don't need air time..IMHO. Your channel of course, but my joy of discovery was somewhat clouded by the ignorant and rude remarks of some.

[@TerrellWSmith]

Hi Sunny Skies, thanks for your gracious comments. As for the complaining, negative, rude and snarky comments, thanks for the suggestion to remove them. So far, I've thought to just let those people show their character and ignorance through their comments for all the world to see. Why a few people feel they must post mean comments, I don't know. I have noticed that other people have posted comments against the ignorant and stupid comments, for which I'm thankful. I feel that people are entitled to their opinions, and I have tried to gently point out when they have misunderstood something. Their comments have also motivated me to make another KZbin video about whether or not a person needs a second 12V battery which can be seen here: kzbin.info/www/bejne/pZfVeqdpjNeaiJY Lately I've run either my Bluetti EB70 and/or Ecoflow Delta Mini from the second 12V battery, and my Dometic CFX28 refrigerator is plugged into one of them. Before leaving on a trip, I make sure the battery stations are fully charged, because as you say, they can take a while to charge and they can also suck quite a bit to charge. Both are made to plug into a car's aux 12V port, so shouldn't draw more than the port can handle (which ought to be around 10A or even less). As you know, my second 12V battery is the same type and size battery as the car's 12V battery. I did that so that the car's charging algorithm would be happy. I do think a second battery should be about the same as the primary battery if the car is charging directly. And most importantly, the same chemistry. If it's a battery station, that unit has it's own charging algorithm, so there's shouldn't be an issue. I sometimes use a "Battery Tender" 4.5A charger and trickle charger if I know I won't be driving for a few days. I got it at Costco. The green light does come on eventually. I find that the automatic charging relay does it's job extremely well. I have a light to let me know when it's paralleled the two 12V batteries, and for the first time, when I had the Ecoflow plugged into the second 12V battery, the light did not come on right away when I started the car. I think because the Ecoflow was sucking so much from the second 12V battery initially. I really like that it's automatic, so I don't need to think about it. A manual switch would work, but it's then dependent on the user to remember to switch it. And what about when you forget? Oops. :) Yes, I still have my same 2010 Prius. It's the most trouble-free car I've ever owned.

[@esamalsharai1854]

Thank you so much dear sir

[@lewis-mindscrambler987]

Appreciate the vid, might do this someday

[@ramjeansakeel8242]

hello sir is this setup doable in hybrid cars with start stop system please thanking you in advance

[@TerrellWSmith]

It should work on any car. The point of adding a second battery, is that if you are running a refrigerator (or something else), you do not want to drain your car's 12V battery, and find you can't start the car. The relay (see at 9:14) isolates the second battery from the main battery while the second battery is being used. But parallels both batteries when charging. Now that power stations are coming down in price, you might consider getting one of those, instead of installing a second 12V battery.

[@ramjeansakeel8242]

@@TerrellWSmith appreciate your ans answer sir but am on an island and its start coming here but extremely expensive am trying to make a box fitted with à relay and a solar charge controller for being able to charge from sun when at stop and engine while driving

[@TerrellWSmith]

@@ramjeansakeel8242 Is the solar on your car? If so, why not charge from solar at all times, stopped or driving?

[@ramjeansakeel8242]

@@TerrellWSmith no not on my car

[@gzhang207]

Nice work and very well presented. How safe and well does the electrical connection hold up in the case of minor water leaks into the trunk?

[@TerrellWSmith]

Thanks, Gary. Good question. But I don't know the answer because I've never had any water leak into the trunk. The cable is a marine grade cable, so it's rugged and shouldn't mind getting wet. I figure if it's good enough for a boat, it's good enough for my Prius! :) The charging relay is also marine grade, and fully sealed against moisture. Both 12V batteries are sealed AGM. So I don't think there would be any problems unless I drive into a lake! And then, as they say, I would have "bigger fish to fry!" :)

[@gotaigo]

Hi Terrell, Although I do DIY stuff when it presents itself, I don’t think I want to tackle this project for safety reasons. Would you consider doing the same setup for my 2011 Prius? Besides the costs of materials, what would you charge for your time?

[@TerrellWSmith]

Thanks for asking, but I wouldn't want to work on someone else's car for the same reasons (safety).

[@AdamGithyanki]

I just want to be able to charge my laptop, phone and sometimes a camera battery. Not necessarily at the same time. I don't think I need a second 12v for that? I could just use an inverter and charge them while the car is in the "on" stage right? This is for if you want to be able to charge sometime possibly bigger like a refrigerator while the car is completely off right?

[@terrellsmith2203]

Right, a laptop, phone and camera battery don’t draw much power. A small inverter that plugs into the aux port will do it. The aux port on the Prius is good for 120W. For things which draw more power, like a rice cooker or small microwave, you can run them off an inverter hooked directly to the 12V battery, with the Prius in “on” mode. This can be up to 1000W. These things draw a lot of power, but only for a short time (20 min. for the rice cooker). But for the refrigerator, it draws low power over a very long time (days), so a second 12V battery is perfect.

[@AdamGithyanki]

@@terrellsmith2203 great thanks

[@dannyjackson1331]

could you do all the same but just use LifeP04 battery?

[@TerrellWSmith]

Thanks for the good question. Yes and no. No: The car charging system is expecting an AGM battery (lead/acid), and will likely overcharge a LiFePO4 battery, ruining it. So you should not simply hook up a "raw" LiFePO4 battery. Yes: IF you use a LiFePO4 battery inside something like a power station, which has it's own charging algorithm for the LiFePO4 battery. The charging station can be charged from your 12V aux port. This is what I'm currently doing to run the refrigerator. My power station (Bluetti EB70) is plugged into my second battery (but you don't need to go this route, I do because I recently got the LiFePO4 power station), and the refrigerator is plugged into the LiFePO4 power station.

[@krisqueen5939]

Informative

[@heidlagedr]

Thanks Terrell for the great info. My question is this, do you find the smart isolator to function as expected? If I was to use the 2nd battery for a while and the car is “off” then with the car in ready mode and start to draw off of the 1st battery until the 201v started to charge the first will the 201v keep charging until the 2nd battery is topped up? I hope you see this and get a chance to respond.

[@TerrellWSmith]

Hi Don, yes, the isolator relay works just like I expected. My experience is that whenever any charging is taking place, from the Prius in "Ready" mode, or from Solar panels, the relay parallels the two 12V batteries. So it's not like it waits until one is charged before beginning the second. If the second 12V battery has been used for a while and is partly drained, but not the first 12V battery (the one that's part of the car), it seems that the Prius charging circuitry senses that charging is needed. When both batteries are in parallel, the "charged" one will float charge to the other. Think water -- there's a connection between two containers filled with water. You partially drain one with the connection closed. The water reserve in the other stays put. Now you start to add water, and the connection opens., Water will run from the full to the one drained so that they both fill up. Normally, if you parallel two batteries, the drained one will "steal" power from the other. That's the beauty of the relay. While draining one battery, they other one stays protected. But while charging, the relay connects the two batteries, and both get charged up. If it is already full, power just flows to the one that needs it. (I'm sure this is an over-simplification, but hopefully it's helpful.)

[@heidlagedr]

@@TerrellWSmith Thanks a lot for clearing this up for me. Safe travels.

[@jefferyorton1723]

Hello Terrell. Great video! I do wonder though.. wouldn't it be possible to charge the 2nd battery directly from the Prius generator/inverter? Any thoughts?

[@TerrellWSmith]

Hi Jeffery, thanks for the question. The way it's set up, the second 12V battery does charge directly from the Prius DC/DC inverter. Whenever there is a charge coming through, whether it's from the Prius or from solar, both batteries are automatically switched to parallel and are charged. That's the magic of the relay. See 9:12.

[@jefferyorton1723]

@@TerrellWSmith Thank you so much for your quick reply. Yes, I can see now they are parallel. However, I ask because I am hoping to make the second battery a 12v 120ahithium battery. I know when making two batteries parallel they must be the same voltage, but shouldn't they also be the same age, material, and amo hours as well? I'm new to this, so any help will be much appreciated.

[@terrellsmith2203]

@@jefferyorton1723 Yes, ideally, it’s good if they are the same. The same voltage, for sure. My second 12V is the car’s original, the other (now the car’s 12V), is new. So their age is quite different, but otherwise they are the same. Maybe someone else can respond regarding your question about totally different types of battery.

[@jefferyorton1723]

@@terrellsmith2203 yes. I now see that they both must be the same voltage, but can be different amp hours. But it isn't exactly clear that they must be the same type of battery whether them being lead or lithium, but I would assume the should be since they have very different charging and dechagring profiles. Thank you for your kind replies.

[@TerrellWSmith]

Yes, you are correct. Different types of batteries have different charging algorithms, and a battery might be damaged with the wrong profile. The way to do what you're interested in is to use a Power Station (Lithium or even better, LiFePo4). The power station plugs into your 12V aux port and it has it's own charging circuitry to take care of the battery inside. The downside is that they are expensive. I recently bought a Bluetti Power Station with a LiFePo4 battery, which works very well.

[@greysonphoenix3442]

Are you by any chance in the PNW? Would you be interested in helping me write my car?

[@williamsmith8760]

I'm adding a fridge that's exactly why I search for this video

[@TerrellWSmith]

Thanks, hope it's helpful. The magic is in the switch which allows both 12V batteries to charge while driving/plugged into solar, and only the second 12V battery to be discharged by the fridge. Another solution would be to get a power station like an Ecoflow Mini or Bluetti EB70S. They can plug into a 12V Aux port, and you plug your fridge into it. I did the second 12V battery thing, since I already had a second 12V battery for the Prius (they are expensive), and the power stations at that time were so expensive, but have gotten much less expensive.

[@skookapalooza2016]

Well done, sir.

[@TerrellWSmith]

Thanks. Hope it's helpful to many.

[@smartsteven123]

Hello, and thank you for the video. My concern would be that the Prius doesn’t have a standard alternator to my knowledge, it charges the 12v battery with a dc/dc voltage converter from the higher voltage system. As such, I would be very concerned with drawing too much current with the second battery, for example if it was drawn down too low or failed internally. I would guess this would be an expensive repair to the hybrid charging system should it fail. Perhaps there would be a way to add a current limiting device with “brains” to control the rate of charge on the second battery? Have you investigated this at all?

[@TerrellWSmith]

Thanks for the comments. You are correct that the Prius uses a DC/DC inverter. As far as drawing too much current, it is fused at 100A. And, the second battery I'm using is a Prius 12V battery. The device with "brains" to control the rate of charge on the second battery is the standard Prius charging system. So far, no issues with this setup.

[@radiospank]

I run 2 amplifiers in my Prius and it’s hard on the electrical at full tilt but been running it like this for 10 years and no problems. Recently I just added a 500 farad supercapacitor to help with that and it made a big difference for keeping voltage at 14.4 when cranking the subs at full volume.

[@caroad2008]

Why doing that? What is the point?

[@Atlanticmoonsnail]

For most of my needs (charging ports and fridge) I have any inverter that works fine.

[@terrycoye3373]

Can you use the inverter when the car is turned off? I think Terrell said that he wanted a battery to use when the car was off.

[@Atlanticmoonsnail]

@@terrycoye3373 No. If the car is Prius then you must leave it in the ready/ accessory mode. The tractor battery will power the inverter and when it runs low the gas engine will kick on. There is additional info on youtube for hardwiring a second battery and switch. I just didn't go that way.

[@terrycoye3373]

Yes, exactly.

[@tanker242]

It's funny right after I replaced the bad AGM batteries in both of my Prius. I realized I could have replaced them with a lithium iron phosphate battery instead.l with nearly twice the capacity. Now, since I've invested in a new AGM battery, that's probably going to last another 8 years. I was thinking about getting a lithium iron phosphate as a second battery to bump up the amp hours close to 150, but I wonder how it'll be mixing the two chemistries together in the 12-volt system. They have different charge curves so I might just have to throw two AGM batteries in one car and invest in the lithium iron phosphate for the V

[@TerrellWSmith]

Yep, you're correct, you do not want to mix battery chemistry. The newer LiFePO4 batteries may have regulating circuitry in the top of the battery to keep them from being overcharged, though. Because your Prius is expecting an older AGM battery, that's what the Prius charging algorithm is expecting. The workaround is to get a power station such as the EcoFlow Delta 3 (or 2) which has a LFP battery, or EcoFlow Delta Mini (if you can find one). These have their own charging system, which you can plug into your 12V Aux port. I do this now to keep my refrigerator going while camping, especially when I'm not getting enough solar (cloudy or rainy days).

[@TheDude10k]

Are you available for a paid install?

[@TerrellWSmith]

No. It’s not very difficult. You can likely find a shop that would do it if you really don’t wish to.

[@TheDude10k]

@@TerrellWSmith you = easy, me = fire haha

[@TerrellWSmith]

@@TheDude10k Funny. :). What I would suggest, if you can afford one, is get something like an EcoFlow Delta Mini or Bluetti EB70S (I have both). kzbin.info/www/bejne/oKKsl5l7oNZ_q6csi=bcmWIbj9TnDBRqG3 They fit nicely in the car, you can easily carry them, and they have power to keep your stuff running without draining the main 12V battery. (I did my second 12V battery install before they were somewhat affordable.) There are many "Portable Power Stations" out there now. They will plug into a 12V port on your car and charge while you drive, plus you can charge them with solar. I charge mine up at home before a trip, then leave it plugged into the 12V Aux port while driving. Hope that's helpful.

[@vaughnsvideos]

You forgot a massive question! Can it be a lithium? LifePO4! Since the original is just a regular vented lead acid and they take different charging profiles than LiFePO4.

[@terrellsmith2203]

Vaughn, that goes beyond my knowledge. Good question.

[@ricecowboy]

I’m wondering the same thing since a lithium battery is much smaller and it would fit in the cubby hole without cutting floor board.

[@terrellsmith2203]

@@ricecowboy , I'm sure you are correct. However, lithium batteries can be expensive, plus I had my old 12v Prius battery available, which still has enough life in it to work. Charging it with the solar controller seems to have "conditioned" it and given it more life. And, as mentioned above, I'm not knowledgeable enough to have wanted to experiment with mixing types of battery hooked to the charging system of my Prius. I knew that the old 12v Prius battery would work just fine.

[@jafinch78]

You'll have to consider being a new video basically dealing with a separate specific charge controller with under and over protection, isolation switch if connection to the vehicle 12V battery as well as other details potentially.

[@nickslingerland4155]

If you added a second 12-volt battery could you add a bigger inverter?I will call you saying a thousand Watts for the small battery could you add a 2000 Watt?

[@TerrellWSmith]

Thanks for your question. Unfortunately, no. The power supplied to the inverter doesn't actually come from the battery, but from the car's DC/DC inverter. The 12V battery acts sort of like a temporary short-term storage place for the power. Think of it like this: If you ran a 1,000 Watt inverter (full load) with the car turned off, how long would the 12V battery last? Not very long before it would be dead and perhaps ruined. Add a second 12V battery in parallel, now the same 1kW inverter at full load would run a bit longer, but now you've killed two 12V batteries very quickly. The power is coming from the car, not the 12V battery. The Prius' DC/DC inverter can safely supply 1kW, but not more. (There is a way, but it involves the traction battery, not the 12V battery, and is a dangerous modification.) Hope that's helpful.

[@nickslingerland4155]

@@TerrellWSmith It was very helpful thank you.

[@nickslingerland4155]

@@TerrellWSmith say if I wanted to make that dangerous modification to the main battery I believe you're referring to. What size inverter can I use then while still not damaging my car?

[@TerrellWSmith]

@@nickslingerland4155 I believe 3kW. If you're really interested in this modification, search on PriusChat. A couple of guys there have done it, and powered their homes during a major blackout. The inverter they use is rather large. :)

[@nickslingerland4155]

@@TerrellWSmith thanks once again. The channel is great

[@caroad2008]

Very well made video.

[@terrellsmith2203]

Thank you.

[@jasonmartinez7667]

Can the charging relay take 70 amps continous? I want to add a sub at 800 rms.

[@TerrellWSmith]

Jason, yes. See at 9:30 in the video, the relay is rated at 120A continuous.

[@engellsd3198]

🙂🙂🙂Thanks for the Video grandpa 👴

[@anthonymarino4260]

GREAT IDEA

[@TerrellWSmith]

Thanks!

[@hotmasked1]

EPIC VIDEO !!!

[@TerrellWSmith]

Thanks for your enthusiasm. :)

[@richardking6066]

A battery for a mobility scooter will work even better - bigger capacity, and ability to deep discharge etc..

[@TerrellWSmith]

Depends on what kind of battery it is, because the Prius charging algorithm expects an AGM battery. The Prius 12V battery is a hybrid, so can also do a fairly deep discharge. If you want more capacity, I recommend a power station which has its own built-in charging algorithm. That way you can use a lithium or LiFePO4 battery.

[@richardking6066]

@@TerrellWSmith Mobility batteries are indeed AGM but, unlike the Toyota battery, are manufactured in much larger numbers and can be as much as half the price for a battery that may have nearly twice the capacity. ie I can pay £150 for an original battery (35aH) or £75 for a 55aH Ritar 12-55, which the maker states has a 12 year design life...

[@supjay3945]

Im thinking maybe space in a cooler/box attached to the hitch, and add solar panel on its top. Only concern is the weight of battery since cooler is on the hitch. Any feedback on this idea anyone?

[@TerrellWSmith]

Hi Jay, that's a creative idea -- however, if you'll be anywhere that has bears, they will quickly shred your cooler. People underestimate the power of a bear. They can tear open locked doors, break out windows, bend car window frames, and rip open very solid boxes (like many people have in the back of a pickup). Another thought is your cooler-solar panel-battery combo might interfere with easy access to the back hatch, but that's something to look into.

[@supjay3945]

@@TerrellWSmith true. Another channel has a hitch and cargo setup. But if I ever try it ill keep bears in mind

[@pangrac1]

Very well.

[@zzzcocopepe]

i am trying to follow along but I don't think I ought to do this on my own. I might try and find someone who can do this for me for a fee. I am thinking of camping in my prius but I want to be able to cook with electric cookware

[@TerrellWSmith]

Cook with what sort of electric cookware? Cooking takes a lot of power. Have you watched my video on adding a 1,000w inverter? kzbin.info/www/bejne/g6uvhXWvq6-KbcU

[@ikolivelongafter]

Hi Terrell! Thank you for such a detailed video. Im currently assembling the supplies from this tutorial and am waiting now only on the charging relay. I was hoping to ask you if the routing for this setup is altered at all if using a 2000w inverter (which Ive already purchased). I perused the comments on this video and understand that the Prius isnt really equipped to go above 1000w. Seeing as I already bought the larger inverter though, should I set it up the same as your video and just not draw above 1000w? My needs dont exceed 1000w, though it was my impression that I should buy an inverter about twice as big as I expect to actually use, and that the second auxiliary battery is installed to allow the inverter to run that higher wattager. Perhaps another youtuber is giving out some wacky information?

[@TerrellWSmith]

Hi Iko, the power is coming mainly from the car's DC/DC inverter, and you don't want to go above 1kW from that. Installing a second 12V battery does not mean you can draw twice the power. (Except for a very short period of time maybe.) The fuse on the car's 12V battery (3rd Gen) is rated at 140A, and on the Gen 2, it may be less, I'm not sure. In an ideal world, 140A x 12V = 1680W, but that's when the fuse blows. Not a good idea. You didn't need to buy an inverter twice the size of what you expect to use, unfortunately. (Hopefully, you got a pure sine wave inverter. That makes an important difference for some electronics.) Generally, a 1kW inverter will have a bit of extra "just in case." A 2kW inverter that you don't need just wastes some power and uses up more space as well. If another KZbinr is telling you you need a 2kW inverter to run 1kW, or that adding a second 12V battery will allow 2kW, then yes, they are giving wacky information.

[@ikolivelongafter]

@@TerrellWSmith Thank you for the reply! Yes there’s a KZbinr PSC camper conversions who mentions buying an inverter rated for twice the amt you intend on using. The inverter I purchased is indeed pure sine wave. I was hoping to power a mobile audio recording studio in remote locations. It’d be an inverter to a power conditioner and plugged into that would be a laptop charger, audio interface, and a power supply for a tube microphone. The wattage required to power those is well below 1000w, i just wanted to be sure I was getting enough. Your video has been vastly helpful!

[@TerrellWSmith]

@@ikolivelongafter Thanks for the info. That's unfortunate that someone is recommending that people waste their money, space, and perhaps put their system in danger by buying an inverter twice the size from what they actually need. A mobil audio recording studio sounds (no pun intended) like a fun project! You can check your wattage draw with something simple like a $30 "Kill A Watt" - you plug whatever you plan to use into it and it'll show the watts you're using. Make sure the car is "On" when running the inverter (so that you don't drain the 12V battery) and that the inverter has space around it for air ventilation. Also be aware that with the car in "On," it will start up and shut down every now and again automatically, so plan for that when you're doing sound recordings.