What happens with Lithium (LiFeP04) and AGM Batteries in parallel ? Let's find out!

We see what happens when you put lithium and AGM batteries in parallel , the answer may surprise you.

[@diconustra]

Myself and some others on the classbforum did quite a bit of work on this a few years ago. I ran my camper on a dual lifepo4/AGM setup with the batteries combined using a Victron Argo diode combiner on the load side and separate charge sources. I also experimented with directly combining AGM and lifepo4. It worked - but for me a simple A/B/Both switch worked good enough and was simpler. I ran from AGM until bedtime, switched to lithium overnight, and charged both during the day. We also drew up circuits that would use an ideal diode to switch between banks, one that would use SSR's, etc. My goal at the time was to be able to yank out the lithium in our Minnesota winters and still have a fully functional camper, without re-wiring. Now I have enough lithium that I don't use the AGM's at all, and I plug the camper in and heat the lithium with internal heat pads.

[@sotasolar]

Nice, that’s quite a setup!

[@realeyesrealizereallies6828]

There is a guy on KZbin, it's called Emily and Clark adventures, he is an electrical engineer who lives on his sailboat, he uses those batteries combined and sells a electrical device to make the process safer..

[@slowbrezze]

Yup even has a device like a reglator but he explains how to for car audionwould benefit from it. But far as th myths he said yes but do the steps monitor and check if balance goes bad that's when it drain from because ppl get comfortable and don't check cells

[@Rj-nh1df]

Nobody wants to spend hundreds on product that you didn't really need

[@pete9501]

Excellent summary. We have been running a hybrid LifePO4 and flooded lead acid house bank on the yacht for two years, works really well. One point worth emphasizing is the lead acid needs to be in good condition. No point in adding LFP to an old end of life lead acid bank hoping it will do miracles. It won't and could cause a problem if the LFP empties its charge into a lead acid battery with a shorted cell.

[@dan32one44]

Good stuff 👏

[@ian-zh6ni]

As you described running differing energy storage chemistries together in parallel makes sense so in the same vein should a discussion emerge about combining super capacitor with AGM or super cap with LiFP obviously in parallel too. I think super caps from say SkelTech ie either 12v or 48v would surprise everyone when combined with similar voltage AGM or LiFP, cheers, Dean, Aust.

[@pete9501]

Excellent summary and fits with our findings after running a LifePO4 and flooded lead acid house bank on a yacht for 2 years.

[@BOREDANDWELLBORED]

So you can mix lead acid and lifepo4 batteries to be charged with the same alternator? Why do manufacturers say it will catch on fire and try to coerce me to spend additional $1000 for dc to dc charger?

[@pete9501]

@@BOREDANDWELLBORED Clarification is required here. Our house bank is a mix of lead acid (LA) and LifePO4 (LFP) in parallel. This house bank is charged with solar and the DC>DC charger from the engine start battery. The DC>DC charger can be replaced with a long cable to achieve the same thing, that is protect the alternator from over heating since LFP will take all the charge an alternator can produce. At lower revs the air flow through an alternator is fine in a car but small yacht engine space will cause it to over heat. Both Victron and Sterling have good videos showing this happen. So either use a DC>DC charger or long cable to regulate the current flow. Alternative solution is expensive external alternator controller, particularly on larger alternators. However, since our primary charging source is solar and the DC>DC only used for occasional top up, its fine for us. Why do manufacturers discourage you from adding LFP to LA? Well someone will try adding a new LFP battery to resolve failing lead acid batteries. That is never going to work. Also they are in business of selling LFPs, not lead acids. ABYC are also rather short sighted and about a decade behind the times. Thankfully those of us not bound by ABYC are free to do what we want.

[@pete9501]

@@BOREDANDWELLBORED Yes, just make sure the lead acid is in good condition. LifePO4 won't fix dud lead acid batteries.

[@BOREDANDWELLBORED]

@@pete9501 so in my solar mppt, do I set the battery charge at lifepo4 profile? Or lead acid profile? There will be 200ah lifepo4 and 100ah lead acid (new) mixed

[@pete9501]

@@BOREDANDWELLBORED You can do either so long as you don't float charge the LifePO4 which will eventually shorten the battery life. I would prefer to shorten the LA life by not floating. Set charge voltage to 14 or 14.2v which will keep the LifePO4 out of the knee for a long life. Some chargers must have a float, in that case set it low say 13.4v. This will provide power for small items like lights without taking power during the day.

[@schussy]

Excellent review. Thanks. The chart showing the cycle of the lifepo4 battery is very interesting. And your arts and crafts illustration .. crude yes, but really good at explaining the power use of the batteries in parallel. Question: Is the charge voltage high level limited?

[@cowboyrolo7892]

I'm looking to do this exact same test with Vmax Tank solar batteries and some lithium for my off-grid shop, Thank You!

[@PropertiesForSaleInJamaica]

What a damn cute dog!

[@eugeneirons7907]

Man thanks a lot. I just bought a lithium Lifepo4 with smart BMS technology and wanted to know if it would work with my AGM battery…

[@user-mm6qe4ks8s]

The EcoFlow power head system for a van is a very easy to set up efficient system. The weakness is it can not take higher amps on a long drive from aux alternator to help charge up 15kwh system. It’s been suggested I use 48 volt AGM bank to connect between alternator and EcoFlow system. It sounds good am I missing something?

[@garyveitch4222]

I do this on my RV. I have a 200aH LiFePO4 battery in parallel with 200aH of Lead Acid Batteries. The majority of the work is completed by Lithium battery. This keeps the Lead Acid batteries in an ideal float charge state 95% of the time. The only time the Lead Acid batteries are drained is when there's excess load or no sun for several days. Of course there's proper switching and fusing between the batteries. The Lead Acid batteries will las a long time in this setup.

[@BOREDANDWELLBORED]

They said you can't mix charge lifepo4 and lead acid batteries in a van alternator. Is that a money making scam?

[@sotasolar]

@BOREDANDWELLBORED you do not want to start a vehicle from lithium. BMS won’t take it. As for parallel systems, it all depends. Healthy lead acid is fine, a worn out lead acid might drain your lithium slowly. If cycling daily it might be fine.

[@BOREDANDWELLBORED]

@sotasolar what do you mean "cycling daily"? I have 400 watts solar panels connected to it. Is that considered "cycling daily"?

[@DavidMccallister65]

You guys are too smart for me. "Just give me the damn number!" 😂😂😂

[@sotasolar]

Sorry, simple version. Lithium will be depleted 90% before the AGM begins to be depleted. Meaning, if you stay above 90% of the lithium’s capacity, the AGM is just backup and draws very little if anything from the system.

[@DavidMccallister65]

@sotasolar I'm just kidding you. Thanks man!

[@geofferyromaldantony3524]

@@sotasolar how about charging ?

[@georgia9969]

Great research, love how yours worked together. I now have 4 AGMs (just lost one that no longer would hold a charge) on my boat that are getting old and will be adding 2 100ah Lithium batteries in parallel. However, I plan to make the following changes to the charging system for extra protection. An external BMS and electronic cutoff switch for the lithium batteries plus a Balmar MC-618 regulator and MC-TS-A alternator temp sensor to prevent my 100amp alternator from overheating when charging this system. Is this enough or do you think I need more electronic protection.

[@sotasolar]

Make sure you have some circuit protection between battery and alternator. For these I like the thermal resetting breakers like this amzn.to/496hfGK This one is only 50 amps, but if your alternator is 100a, I'd not want to be pulling close to that for too long. I'd look at protection on both ends, because you could overload from alternator side as well as battery side.

[@boan1502]

Other use for Li-batt. in parallell with Lead is in boats, if you have charger’s for Lead and don’t want to change all of them. What is your preferens of sizes between Li/Lead 50/50% or ?

[@checkitoutguy3155]

I have a 48v 100ah (5kw) LFP Battery and a 48v 200ah (10kw) Sealed Lead Acid battery bank (4 x 12v 200ah) connected in parallel to my 10kw charger / inverter. They were connected when their voltages were the same. They charge and discharge in unison and their voltages remain identical (to within 0.01v / 0.02v) throughout. The battery low voltage disconnect cut-off is 48v, so c.10% for the LFP and c.48% for the SLA. The LFP charge voltage is 58.4v, the manufacturer's suggested SLA charge voltage is 58.8v - 60.00v. It seems to work ok and I have not noted any abnormal signs, the only thing is that the SLA batteries are charged to c.53.2v when at rest, when the suggested level is 52v, so I guess that will impact the SLA bank over time ?, but in the meantime, it means I can use them with my LFP battery and get another 5kw of usable battery capacity, otherwise they would just be sitting there doing nothing.

[@jorgeheny3867]

Lead acid battery is a good protection for charge controllers in case of lipo4 BMS shut down .

[@user-wq4ke5qo8m]

And what about the Charging at the end ? Please explain somewhere

[@Mongoose069]

lifpo battery allows for steady uninterrupted power *while in its nominal SOC and within working capacity limits AGM allows for further uninterrupted power due to the deep cycle capability and available high cranking amps So while standard battery theory suggests these two would NOT compliment each other, they actually compliment each other rather well in MOSTLY a passive way. the AGM steadily maintains the SOC on the lifpo battery but will "assume the majority of the load" should the lifpo battery fall below it's preferred working limits. long explanation shortened?

[@johnnypiper1717]

Awesome video, i was thinking of adding a lifepo4 lithium 22ah battery to my car audio system. I habe a xs power 100ah agm under my hood and heard people say i need an isolator and heard with lifepo4 lithium and a good agm its ok to habe the 2 chemistries parallel with each other without an isolator. I will always habe my truck running when my system is on and plan on atleast once a month putting both batteries on a charge to keep them topped off. From watching your video it seems its ok to run the 2 parallel without an isolator is that your thoughts? Thanks

[@sotasolar]

With car Audio it can be a bit different because the amps that those batteries produce is much more than the RV ones we use. AGM and Lithium are very similar. I think you’ll be fine for a charge and discharge perspective, just make sure you have proper over current protection.

[@johnnypiper1717]

@sotasolar 10/4 yeah I plan on running from my front battery(agm) through a 300A fuse then to my lifepo4 lithium battery off it through another fuse then to my sub amp. I heard the lifepo4 chemistry and good agm batteries resting voltage was pretty close to not really worry about putting an isolator. Plus I figured I'd put them on a charge once or twice a month jus to make sure there always fully charged

[@michaelharrison2775]

I don't know why people overlook this but lithium iron phosphate has less internal resistance and it will draw down first and then start drawing from the lead acid it will also charge up first but there's less difference in the newer lead acid carbon lead acid and AGM charge more quickly than your conventional lead acid batteries

[@raducumilea-is2yi]

Hello how about Agm and lipo4 in parallel and series...? 24 volts /48 volts? How they will suport the charge amd discharge? What oarameters to set on them? Thanks!

[@sotasolar]

I suppose you could in theory parallel those separate banks, but I would not recommend it. You have to have external balancing. Or maybe I should actually test if you need that balancing.

[@notreallyhere7719]

So the lithium would trickle charge the agm to equalize batteries? So when both fully charged, the agm would draw current to keep the batteries at same voltage? Were lithium is, at higher. Voltage.

[@sotasolar]

What we found is the amp draw is negligible from lithium to AGM to about 30% SOC for lithium.

[@JohnDoe-fk5fr]

I run three optima’s and one lto 6 and it works fine for my stereo in my vehicle. I want more power for my amp and was thinking of adding one more lto 6 for burst power but the ds40 is on sale and really good price right now. The ds40 is lifepo and they don’t recemend running it with agm or lead acid they say do a battery delete. What is the difference between running lto with the optima’s and running lifepo with the optima’s?

[@sotasolar]

For car audio, LTO is much better I believe.

[@BoobeeMyles]

Could I add a lifep04 as a 2nd battery in parallel with my starter yellowtop for my car audio system?

[@JohnDoe-fk5fr]

@@BoobeeMyles I believe they suggest using a battery isolator but I have seen it done. Basically as far as I know lto can run with agm but lipo needs an isolator. I think it boils down to standing voltage when it’s all off. So one doesn’t drain into the other. My Lto stands at 12.8 I believe and the agm will stand at the same at full charge. Like I said, I seen it done but who knows how long it lasts. My lto6 runs with the three optima’s with no isolator. I’m no expert though so keep asking.

[@sotasolar]

@JohnDoe-fk5fr the testing we did here shows only a few amp hours flow from LiFePo4 to AGM at rest over a 24 hour or so period. Pretty much a rounding error. I can definitely see some value in an isolator all the same, I just don’t know when and why to isolate. AGM kind of acts as a ballast.

[@anythingwewant604]

My lithium is 13.8v and agm 12.6v I’m debating on running 2 separate systems. Agm for lights and 12v power outlets and lithium larger things like heat fridge ect. Would it hurt to wire them in Parallel for charging?

[@sotasolar]

Won’t hurt anything. I’d try running them together and see how it goes. Do report back!

[@pete9501]

We have been running LifePO4 and flooded lead acid in parallel for 2 years on the yacht. It just works brilliantly.

[@myhificloud]

LiFePO4 prefers to live between 30% - 80% charge to ensure full cyle duty without degradation. If LiFEPO4 is well taken care of during it's life, calendar aging will be your biggest challenge over time, with simply a reduction in runtime over the years. Impressive chemistry.

[@thriveforbest3217]

Sir i need help 😊🙏 can i use just 6x45ah lithium cells and remove my AGM battery from the car audio? I running standard alternator too. can it work without issues?

[@sotasolar]

I don’t have much experience using lithium in car audio. I do know they typically use a different technology and not lithium iron and phosphate.

[@conandrum74]

Hi great video. Maybe you can help me with your own experience. 13 years ago I built a CTEK based dual battery system in the car for camping. Once while camping, the car battery went low from the car being open too long and a person got stuck inside. Since then I modified the system to include a BEP motorized switch with remote so I can connect the starter with the 2 service batteries in parallel (all AGMs). 5 years ago I replaced the 2 service AGMs with 2 LFPs (Relion drop-in replacements) and never thought nothing of it. Nothing else was replaced and everything has been running just fine. Since then, a few times every year, I have jumped the 2 banks with the BEP switch with no ill effects. The voltages combine to around 12.9V if memory serves and I think I even started the car with them joined. I never had any issues. Both banks charging with the same AGM charging profile using the alternator or AC-DC charger. Of course CTEK support is adamant that I should be using a Lithium charger because during DESULPHATION stage#1, the voltage reaches 15.8V and this may cause LFP BMS to shutdown the LFPs (I never noticed such a thing). Relion said that the worst thing that can happen is the BMS shutting down the battery - never happened. Another thing is that my AGM lasted 9 years and was replaced 2 weeks ago - the LFPs may have largely contributed to this by constantly trickle charging the AGM. One fine day, the AC-DC charger just refused to charge it, and I thought it blew its fuse, until I checked it and it was fine! Assumptions: 1. It is probably better to have a Lithium program to charge LFPs. The AGM program may not charge the LFP fully. I do not have a shunt to verify. 2. In some application it may be better not to trickle charge the AGM from the LFP, thus slowly emptying the LFP. Some competitors to CTEK have voiced their disagreement as folows: "the ability to back-feed charge to the main battery is actually a defect in the design of the D250 - they actually cannot stop it so they made it into a feature. In the case where your service battery is Lithium and the main battery is lead-based, the Lithium will discharge into the main battery even with the system off. This is because a lithium battery voltage is always higher than that of a lead-based battery. This now means your service battery will discharge into the main battery." However as I already said, it may have actually contributed to the AGM longevity - I do not know how much of a depletion this had on the LFPs daily. My car sits for up to a week sometimes and the LFPs are always on 13.2V - so no ill effects afaik. 3. I wonder if it is dangerous to connect a depleted AGM to full LFPs... Is it possible that the AGM may require a large portion of the discharge current from the LFPs ie. >75A from each LFP? 4. Many sell relays for battery connections... I use a Heavy Duty switch. That should be absolutely OK right?

[@sotasolar]

Whew, lots to answer here. I’ll give my $.02 . When using lithium to jump your starter batteries I’d connect them for a while to boost and then disconnect before starting . Like you stated, the resting voltage of lithium is higher, so some amps will flow. Now you’ve been fine starting as-is, so YMMV. Keep in mind when hearing feedback from a manufacturer, they are looking at liability and warranty scope. Anything they endorse is now on them, I’d doesn’t mean it explicitly will or will not work. They cans account for all batteries in all situations. If connecting a depleted AGM to lithium, it could be an excessive draw for a moment if the battery is down to 5-8v or something. But if it’s resting at 11 or 12v there just isn’t the potential to draw 150 amps or something. Lead acid battery resistance is high at top and bottom of charge. On the topic of need a lithium charger. The BMS will protect from any over voltage conditions and if there is an under charge it will be slight. I use AGM charging modes to charge lithium often. Sounds like your solution is working good.

[@conandrum74]

@@sotasolar can you touch on point#3 ? Any comments?

[@sotasolar]

For the sake of posterity, I updated my original comment.

[@thvestergaard]

I have/will have a similar setup in my camper. It came with an original 100Ah AGM battery running existing 12v system. I just bought 200Ah LiFePo4 and a solar charge controller for LiFePo4 plus 2 150w fixed panels and a 150w temporary flex panel. I will mount a switch between the batteries + pole, so I can temporarily disconnect the batteries. When disconnected I can solar charge the LiFePo4 with up to 14.8V. I think that is too much voltage for the AGM. I plan to let the batteries work in parallel both in the evening to charge the AGM with the LiFePo4 and when I will run the campers AC. I plan to mount the 220v inverter on LiFePo4 + and the - on the AGM battery for the AC. AC will draw up to 900W and if using both batteries, it will lower the power draw, compared to only running it from the LiFePo4. It can not run using 900w for too long, but when the camper is cooled down, it will draw less. Any thoughts regarding this setup?

[@sotasolar]

I’d leave the batteries connected and run the AGM charge profile. Lithium will stop accepting charge at all at 14.6v and really, anything above 14 volts is about full for lithium. Search the google for “lithium battery charge curve “ to see what I mean.

[@patrickbrideauful]

Is the solar charge controller is set to lithium?

[@sotasolar]

Yes. There isn’t much magic between AGM and lithium. It’s mostly the shorter absorption time.

[@stefanusshilongo71]

Can you connect a silver calcium with a AGM in parallel

[@sotasolar]

No idea. It’s all about working voltages. Lithium is slightly higher so it works good there

[@Silentjustin06]

Does anyone know how a lithium in parallel with a AGM would perform in a car audio setup? I have a AGM under the hood in parallel with a AGM in the trunk to run my amps. Can I connect a lithium in parallel between the 2 AGM batteries to help keep my voltage from dropping?

[@sotasolar]

I’d think that would be fine. BMS may trip depending on on amp load.

[@Silentjustin06]

@@sotasolar ok thanks, the amps draw around 300 to 350 amps

[@myhificloud]

@9:35 12v Battery charger parameters are programmed at different levels for various battery chargers (e.g. lead acid, AMD, LiFePO4). Using a standard battery (car) charger will never allow a full charge of your LiFEPO4 Characteristics 12V Charging Voltage 14.2~14.6V Float Voltage 13.6V Maximum Voltage 14.6V Minimum Voltage 10V Nominal Voltage 12V/12.8V 12V Sealed Lead-Acid (AGM) Battery Voltage 12V sealed lead acid batteries, or AGM, reach full charge at around 12.89 volts and reach complete discharge at about 12.23 volts. 12V flooded lead acid batteries reach full charge at around 12.64 volts and reach complete discharge at about 12.07 volts.

[@diconustra]

AGM's need to be charged to a voltage >14volts to be considered fully charged (Deka recommends 14.4-14.6 at 68F). They will settle to a resting voltage of around 12.8 after the charger is disconnected. A full discharge of an AGM would be to a resting voltage well under 12.0 volts - I.E 11.5 - 11.8 volts. A discharge to a resting voltage of 12.07 leaves about 25% of the battery capacity unused. AGM battery life is shortened somewhat by deep discharges though. A standard lifepo4 charge profile is compatible with AGM's, though not ideal, and a standard AGM profile is compatible with lifepo4, though again it's not ideal. Using a standard lead acid profile with either AGM or lifepo4 though, will cause problems if the profile includes a desulfate phase.

[@myhificloud]

@@diconustra This is great information, thank you for this.

[@MichaelHigginsJR]

Considering using my yellowtop to start the vehicle in parallel with 3 100ah chins lifepo4 with 1kw solar.

[@sotasolar]

Make sure to put a 50-100amp thermal / resetting breaker between the two. You don’t want to cook the BMS in the chins. Been there. Your starter may ask for 1000+amps on start. Lead acid is great for that, not lithium with BMS.

[@americannumber2]

Lfp resistance is very low. Small Voltage difference cause large amps flow into lfp BMS can cut off

[@sotasolar]

Sounds like something else to test :-)

[@notreallyhere7719]

Like seeing these experiments/ tests. Thanks. If the voltage of agm was around 12 or lower Around 40% capacity. And u hooked up fully charged lithium curious to see what the transfer of smps would be.

[@conandrum74]

@@notreallyhere7719 me too. That kind of worries me.

[@kennedymallery665]

I think most people getting into lithium is coming from AGM’s. I’m sure this question has crossed many peoples mind. I know it did mine. Thanks for the video.

[@myhificloud]

Sharing some experiences, not everything may accurate/apply to your use case/application: @6:58 Lithium & Lithium Iron Phosphate (LiFePO4 battery) without a BMS and at half/full charge, has the potential to become an arc welder. @7:29 Winnebago and other coach manufacturers generally have a dash mounted battery bank combiner button (temporary connect) for this exact purpose. The temporary action of the button ensures the safe operation of less than 5 seconds use to start the engine, ensuring you don't cook your battery cells (sulfides) or equipment/conductors in the chain. - Any more than ~5 seconds and you'll likely cook equipment/conductors in the chain. - If you intend to replace your coach AGM with Lithium Iron Phosphate (LiFePO4) batteries, you'll need to reduce that time of use (battery bank combiner function/button) to less than 3-4 seconds, depending on the LiFePO4 BMS discharge rate (e.g. 100 Amp, 200 Amp, some are now 600 to 800 Amp discharge for dedicated LiFePO4 starter batteries). The higher the amp discharge introduces a higher probability of magic smoke/fire the longer you hold the button. @8:38 In this scenario, there are two battery banks at different voltages. Without regulation/balancing equipment, the two battery banks will seek (inefficiently) to balance all cells, drawing higher voltage (starter battery) in this case, to lower voltage (Lithium Iron Phosphate coach battery), thus potentially draining your starter battery to a level insufficient to start your engine. Potential AGM Degradation (Sulfated corrosion): Now, what if you reverse the voltage levels of the AGM (lower voltage) LiFePO4 battery (higher voltage), will you eventually cause premature AGM degradation (sulfated corrosion, although AGM is less prone to this issue) to your AGM cells due to the LiFePO4 battery maintaining constant float levels of the AGM cells? Side note: LiFePO4 Battery Isolation Manager (BIM) If you don't want to cook your unregulated alternator while high idling or driving, Battle Born offers a piece of equipment that charges your LiFePO4 battery bank for 15 minutes and at half the capacity of the alternator output, then shuts off (cooling) for 20 minutes, continuing these charge cycles until reaching a LiFEPO4 charge of 13.4v is reached, or if required it will safety disconnect at 14.4v.

[@sotasolar]

Good info here, thanks for sharing. Maybe I’ll go into detail sometime on my bus system. It’s a 270a @24v alternator. I adjusted the voltage down to about 28.0 no load. So lithium bank never receives more than 100a charge. I have a 500a BMS in it. Works good . I still disconnect when starting with a breaker.

[@myhificloud]

@@sotasolarThank you, all of your videos have been helpful, great info and very much appreciated. It's a community effort, learning every day. Thanks for the great content.

[@myhificloud]

​@@sotasolar This will ensure great care on the entire chain. We are following the .2c charge/discharge (of full battery bank capacity profile (1200Amp Hours (14400 Watt Hours) x .2 = 240 amps)to ensure full life cycle duty, until either discharging below freezing without preheating the cells, or calendar aging. As the batteries top off, BMS #1 disconnects changing the .2 rated charge profile considerably for the 3 remaining batteries charging, until #3 BMS disconnects and so on. Charging at a lower amperage ensures .2 charge rating is achieved, yet requires longer drive/alternator/generator/solar run time time to match. Always an adventure.

[@diverd2162]

This set up will void any Lifepo4 warranty

[@sotasolar]

It’s extremely common and even recommended now to pair an AGM battery as a dump load. On the warranty side, in the US the Magnusson Moss Warranty act puts the burden of proof on the company for proving an act caused damage. Most warranty void if removed stickers are not enforceable.

[@OnerousEthic]

I didn’t come here to watch a dog video…

[@sotasolar]

In MN we call that a twofer :-)

[@christophkaiser]

I have a 12-volt lifepo4 and a 12-volt deep cycle. I ran them both down to 12 volts, then I put them in parallel and hook them to my solar charger. I just did that today. My worry is that the resting voltage of the deep cycle Battery is 12.6, My theory is that it's going to drag my lithium all the way down to 12.6 When resting. 12.6 on a lithium battery is like 15%. Which essentially could mean I will lose 85% of the batteries at rest, if I didn't have sun for a couple days and didn't use power it Will leave my lithium battery at 15%. losing 85% of its power Just sitting there. Which would mean I have about 70 amp hours of usable energy, instead of 150 AH.