Is It Safe to Parallel different size or age lithium RV Batteries?

We often wondered what actually happens when different size or age batteries are put in parallel. So we decided to find out!
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[@lukefarmer5391]

I’ve been running a diy 300ah and a chins 100ah in parallel for about a year now with no issues. I’m also running three diy 300hr batteries in series for my 36v trolling motor for over two years now with no issues with imbalances. Great video👍

[@joshm3342]

Fabulous test! The graphical display made things super clear. Thanks.

[@BK-dv1hh]

Honestly, I thought things might be much worse for the smaller battery…however, to hear that there doesn’t seem to be any real concern doing this..didn’t expect that summary of the experiment! Lots of time I don’t understand what the data means, but you always summarize in the realm of practicality. Very appreciative of that. Thanks

[@daviscrt]

I thought for sure the larger amp hour battery would not fully charge. Great video. Don

[@TheRenoir]

Love watching different YT channels experimenting with various configurations of batteries. Much knowledge gained from your efforts. Thank you.

[@familyrvliving]

I love your videos. I like that you tell you the facts instead of telling people they should just by more batteries and replace what they have already.

[@DaveSquibbSr]

Batteries running parallel are always going to equalize, great experiment I enjoyed watching it 😎😎

[@marcobrian1619]

IV got 12 cells at 200ah..at 12v set up. So IV one at 400ah and another at 200ah. Yes time to time I do kick the power on....rest of time I'm a ,3c discharge. Time to time I measure the voltage in each cell.... My deli bms's seam to keep them well balanced as I'm 100/200mv out. I'm using a fluke 112 in calibration to test with. Great information clip there....thank you.

[@jerrygundrum1]

been doing this for a year or so......been working fine. voltage is the constant

[@tyfarquhar]

Really interesting video. Thanks!

[@MrDkgio]

Both batteries will charge and discharge at same percentage, ie if 30 ah drain, small battery will give 10 ah and larger battery 20 ah (roughly due to being 206 ah)

[@rottweiler9535]

running 2 home built battries, 450ah and 240 ah, the bms's take care of everything, and the amperage gets shared, i ran a 2000 watt ac load approx 200 amp dc as a test until the bms's shut down, works fine.

[@galen__]

I’ll guess the voltage during the flat area of the charge/discharge curve will match and the amps will be 32% to the 100Ah and 68% to the 206Ah. The areas 0-20% SoC and 80-100% probably will be different because of internal resistance of each battery and any additional resistance in the path to each shunt 😅

[@sotasolar]

I think you’re pretty close.

[@mortaneous]

Great video! Very informative. With regards to your recommendation to not series up batteries to get the target voltage, my 24v system is using two 12v 200ah batteries in series (exact same batteries) and have been using it for about a month now. No issues so far. I top balanced them as best as I could before connecting them in series and I got their voltage to within 20mV of each other e.g. one is at 13.43v while the other is at 13.41v. A month later, they're still 20mv from each other. So far so good, I guess. Will revisit their status and health in around 3 months maybe. I plan to add another battery then - a 24v 100ah battery from a different manufacturer. I'll connect it in parallel to the two series connected 12v batteries to increase my total capacity to 300ah.

[@sotasolar]

Glad it’s working out so far. We’ve installed a few systems with that configuration. We do recommend a battery balancer then, Victron offers one. Check the battery voltage near top of charge, that is where you’ll see the difference. Use the mid point sensor on the shunt to log the data in the cerbo if you have one. It’s a good indicator of it will be an issue. If you keep your absorb voltage around 28.4 or so, you should be fine. At 28.8-29.2 it might get tricky with one battery cutting off charge before the other.

[@ww-eg2gn]

Can I run the same size lithium batteries from different manufacturers in series, parallel? I have 2, 12 V 100 amp Li-time batteries and would like to buy two more of the different brand( from a friend) and put them together in a 24 V 200 ah configuration. Is that safe?

[@sotasolar]

I’d say I’d each series pair is matched, you’d be fine. That said, you need battery balancing to keep the mid points balanced.

[@PhillipMikeHunt]

Check they can be run in series. Some bms won't work. The batteries will drop down to 12v Check with the manufacturer. You can run in parallel but check the batteries are within 0.1 volt of each other before connecting or you will get a big amp transfer as they try to equal to the same voltage and you could let the smoke out of the cables.

[@charlieakers1522]

Super awesome tests and graphs to show real time data, excellent job. Have you played around with connecting a LifePo4 with another battery which is at a different state of charge to see what the "leveling" current would be between the 2 batteries(either w/ AGM or another LifePo4)? This is a test I am planning but you have way cooler sh!^ to do testing with, or maybe you've already tried this? Love your AGM/Lithium icehouse idea and might have to borrow that idea up here in Alaska! I am in the design stage of changing my boat over to Lithium and am curious how far apart the DOD of each could be and still combine 2 separate banks without the ah flow between the 2 trying to balance would be an issue. I have been leery about having a switch which lets the 2 banks touch one another for fear of overshooting a 1C charge rate in or out of the different banks. (Short explanation for those scratching their head as to why 2 sets of house batteries- 2nd banks main purpose is for a 36V troll motor/anchor hold which is switchable from 36V to 3-12V 100ah batteries to use as house power as well)

[@diysolaradventures7894]

Hey its been a while I have a question concerning mixing battery banks can I use my custom built 24v 280ah Daly bms battery bank with this 24v 100ah lithium battery I bought off ebay can I use both together as one bank for my solar and the smaller battery will reach 100% first and simply wait on the bigger battery to reach 100% ?

[@sotasolar]

Yes, I don't see a problem. I would put a fuse / breaker between the banks.

[@diysolaradventures7894]

@sotasolar oh ok thanks

[@deanshaw7434]

I currently have 4 12v 100ah lisuateli lifepo4 batteries in parallel, and have ordered a lisuateli 12v 200ah battery. I've seen a lot draw down testing videos like this one. I don't understand why nobody is testing 2 100ah running with 200ah. I would think that results would be much closer when capacities are matched.

[@gregmay9097]

So what are the discharge stats of each battery when tested seperatly for comparison to when they are paralleled? What is the internal resistance of each battery and is this affecting the discharge/charge rate?

[@jorgeheny3867]

If bms fail , AGM will protect solar Charge Controllers for battery voltage loss , when solar is charging.

[@sotasolar]

Great point

[@jec_ecart]

Yes

[@jeffegg2]

I think all you are seeing is the imbalance between the batteries... were they both balanced at 100% before the test??

[@jec_ecart]

Those charts are very confusing. How much total capacity did you get?

[@JR-kk6ce]

Hi, great video. I have a suggestion, though. This is a bit of a technical video. So, in my view, you might want to state your conclusion at the start of the video. Then, support your conclusion with evidence, and finally, restate your conclusion at the end. The best way to convey technical information is to think of it as a Christmas tree. You start by stating your conclusion. Then you present your facts, sort of like hanging the ornaments on the tree. Finally, you restate your conclusion to leave, no doubt, as to what you were conveying.

[@GrahamMcDonald-mavrix]

Thanks, What size fuse would you recommend putting between the banks please?

[@sotasolar]

Equal to or less than what the wire is rated for. If using 2/0 wiring, 200a or smaller (too small and it will blow prematurely) .. if 4/0 cabling, 400 amp or lower, like 300 or 200 .

[@GrahamMcDonald-mavrix]

Do you think it's safe to add two new 150ah lithium po4 to 2 year old 2x 120 ah lithium po4 in parallel. 400 amp shunt in existing buttner system. Appreciate your opinion. Cheers Graham

[@sotasolar]

Absolutely! More and more we’re thinking about current protection between battery banks. So we may want to look into putting a separated fuse between them. But other than that. It’s fine.

[@howardescoffery4950]

My brother awesome video. May I ask a question though? Did you let the batteries sit for about a day and equalize? I wasn't sure if that was apart of the evaluation.

[@wheathavester6562]

I have 2 200ah 12v lithium batteries. I connect in series to make it 24v. Then I plan to buy another 24v 320ah lithium. I will connect this 24v battery to the former 12v banks. Is this ok? All batteries are from the same company. I don’t care one battery charge another battery a little. My concern is it won’t damage other equipments such as charge controller, inverter.

[@richmurphy5647]

Hi there I have a question about my battery relocation from the tongue of my 30 amp Northern Spirit 2649BH. Moving 4 X 100 ah LiTime minis to behind my tv which is about 1/2 way down the rig. I will be installing a Victron MP 3000 watt also, I know I need to connect to the fuse panel to the batteries but how would you do this ? Would you tie into existing cable somewhere as there needs to be power to the tongue area for power jack and break away cable. Thanks for any input

[@sotasolar]

I’d recommend using a bus bar or Lynx Distributor to connect your batteries to the Multiplus. Then run a separate fused 6awg line to the tongue or to the DC distribution panel, whichever is easier/ closer. This will energize the tongue jack and brakes.

[@richmurphy5647]

@@sotasolar Thanks for your reply, I do have the victron 6 way mega fuse holder and I do have 6 awg OEM wire that is already there from the OEM batteries. Can I tie into this line as there may be other 12v items that feed from this wire. I have one renogy 100ah battery I was going to run off the tongue which will be hooked up to my 100 watt OEM solar.My battery disconnect switch is in front cross beam do I disconnect this? Sorry for all the questions, I do have the explorist life plans that I’m going off of.

[@sotasolar]

@@richmurphy5647 In this case our philosophy is to simulate the old battery location by extending the 12v 6awg leads from the Lynx or Bus bar to the old battery location. This ensures everything still works as intended and we feel keeps the system understandable to others who come to work on it after us, such as RV techs or owners. We'll often use some heat shrink tube to cover a bolt and nut that connects the two systems together. Almost all of our trailer install videos cover this (5th wheel work differently many times).

[@sgtusmcarch]

I have 2/ 100ah batteries and 1/50ah, for some reason I thought it was not safe to parallel them together. What do you recommend? to have the 50ah in the middle or at the end?

[@adassociates8235]

What about when charging both batteries? Are they being charge as same rate? Thanks

[@sotasolar]

They both get full. Lithium fills first, then AGM tails off.

[@adassociates8235]

@@sotasolar for example with 50A charger, will 200A lithium battery charge first then 100A lithium or they are both charge with 50A same time?

[@justukas1980]

Well if u have a Lithium 200ah and 2 agm batterys. How do u set it up to use the Lithium battery until it's needs the agm batterys. Is there A specific way you need to set it up.?

[@BradLMN]

Very interesting video. I have 2 200ah Enjoybot batteries for my 5th wheel. I also have a 12v Victron Multiplus II 120, solar chargers, & smartshunt. (basic description of setup) I would like to at least double my battery bank. My existing batteries have been in use for a little over a year. Only have had about 4-6 discharge cycles on them. The rest of the time, they have been on standby/maintenance charge. In the winter months they aren't used. So, my question is can I add 2 more of the same to the battery bank without harming any of the batteries? What would happen if I did that? I know....batteries are better off being installed together at the same time. Just thinking it might save a little money if I could just add 2 more. If not, then going with 3 of their 280ah versions will do the trick if I have to go the route of same age batteries.

[@sotasolar]

You’re fine, add them. If it works fine with a battery double in size, one 1-2% different will be just fine.

[@BradLMN]

@sotasolar Sounds great....thank you! Hopefully, we are done with sub-zero temps in MN now....🥶 Although we have had a pretty easy winter so far.

[@lukefarmer5391]

Installing new batteries together really only applies to lead acid batteries. You will be just fine adding additional batteries of different age and ah ratings with lifepo4 as long as they are in parallel.you can do it in series as well but they all must be the same or close to the same ah rating.

[@BradLMN]

@lukefarmer5391 They will be the exact same batteries. Of course, the manufacturers usually say only within the first few months or so. Lol

[@sotasolar]

@BradLMN imagine a company selling batteries having a recommendation that favors the sale of more batteries? :-) Some recommendations are well founded, this one, I do not see it.

[@dowlutteeasooreeanand1355]

is it possible to parellel LIFEPO4 pack and Lithium iron NMC battery pack together with solar inverte

[@marka9083]

I'd like to know how the same test would go if the load is greater than the larger batteries max discharge and also if the charge current is more than the max charge

[@sotasolar]

If sustained I’d expect a cascading protection mode shutdown from the BMS. I’m not opposed to this, but what would be the use case?

[@marka9083]

@@sotasolar Running a high load like convection microwave or AC that could exceed one battery max discharge seems like a valid use case. Similarly if your inverter charger puts out a max current greater than one batteries charge limit but well within the two batteries, you could exceed if one reaches fully charged ahead of the other.

[@sotasolar]

In this case we’d have to add more batteries. We recommend 400a of discharge and 200a of charge capacity. I might be missing the point of running this test under conditions that would likely cause the BMS to fail. If killed a few myself :-)

[@marka9083]

@@sotasolar I was just describing a valid test case where dissimilar batteries could "fail" to perform.

[@angacamthehobbit-PapaPrepper]

How many lithiumn batteries can you run in parallel? I have (2) 200 amp batteries and also just got from a friend (2) 100 amp lithium batteries, Can I add a total of 6 batteries all in parallel if I got 2 more batteries for a total of 800 amps. Thanks Andy

[@sotasolar]

With circuit protection between each battery, and overall protection for main wires it’s unlimited in my opinion.

[@BrianThompson-c8w]

Is there any BMS in those batteries. They control charge and discharge. So no problem

[@sotasolar]

Yes, SOK and Li Time both have BMS. I agree, BMS makes the battery very tolerant of abuse they might not otherwise be.

[@BrianThompson-c8w]

@@sotasolar the BMS is critical. I build my own batteries with CATL or Eve cells and the BMS is JK. I thew the nice looking Daly out of the window because of bad balancing and no updates

[@rvingonthego]

How would it look if you added another 100ah battery

[@sotasolar]

I'm assuming adding it to the other 100ah, so you'd have 1x 206ah parallel with 2x 100ah ? I suspect it would not be 100% equal because of different BMS and internals, etc. One of the goals of this test was to show what happens in worst case scenario and to see how critical it is to do this or not. If you mean adding the additional 100ah battery to the 206 side, I suspect the affects would be compounded further but in the end still be workable for a load like this.

[@larryphillips4164]

So really the only problems would be over an extravagant amount of time (years) for the smaller battery getting slightly cycled more and balancing from the larger battery. So really if you’re fine with loosing 1 or 2 of your expected 15 to 20 year batteries life then it’s probably ok to just parallel lifepo4 battery brands.

[@roadtrippingdrone5139]

does total AH go up?

[@sotasolar]

Technically yes, but I’d not add the AGM capacity to the overall bank

[@chris_mk5supra]

Amazing still people think you should not do that ... Doing that for years and no issue .

[@milesmccarty1005]

You need to understand how resistance affects current flow to and from as well as the grade of cells/BMS/Internal wiring.

[@gregfabian4655]

Question, Can you run to battery one 48V and one 51V in parallel?

[@sotasolar]

I’d be curious to see the exact make and model that you referencing but in general I would not. We have successfully paralleled, lithium, and AGM without a problem, and those do run at slightly different voltages, but with the same charge profile, they still charge up equally.

[@gregfabian4655]

I got one Aolithium 51.2V 100Ah 5120Wh and one it’s TTN 48V 100Ah 4800Wh i’m trying to run them in parallel but doesn’t work. The inverter is using it the 51 V battery first and then start using the 48 V once the first one get to about 15% of usage

[@sotasolar]

@gregfabian4655 that’s similarly to how AGM and lithium work when paralleled. You may need to adjust low voltage cut off down on the inverter.

[@gregfabian4655]

Thanks for your tip. I will try that I believe that will work.

[@jeffegg2]

should be the same as if you paralleled three 100ah.

[@jec_ecart]

You'll get roughly the full ah capacity

[@digicabtech]

I collected a large number of USED lithium 18650 batteries from different brands. I want to build a new battery pack 8S10P (8 series by 10 parallel) for my e-bike. I have set up each battery bank with the voltage as close to each other as possible. 4.199 volts to 4.100 volts throughout 8 series. eg: bank01: 4.199volt to 4.190volt (10 batteries in parallel) bank02: 4.189volt to 4.179volt (10 batteries in parallel) .. bank08: 4.119volt to 4.100volt (10 batteries in parallel). The total voltage for the pack will be approximately < 33.6 volts. Because they are USED batteries. Therefore, they have different voltages and ampere. (Generally, 18650 batteries are 4.2 volts at max. Due to it being USED/OLD, therefore they dropped the voltage under 4.2v each. *_1) Do you think it is safe to mix the batteries with different voltages in PARALLEL, where the different voltages deviate in 1/1000?_* *_2) Do you know what the SAFE DEVIATED voltage is when connected in parallel?_* Please advise. Thanks

[@sotasolar]

I’m not an expert on 18650 battery pack building. I’d say capacity is more important than voltage. When I did pay attention to DIY packs it seems important to group your cells by capacity. And you want each battery in series to have the same or similar capacity. The lowest capacity cell group will define the usable capacity of the battery as a whole.

[@nelsoncruz7278]

If both battery are parallel Both will drain down at the same time

[@M.Bassin]

Draw evenly to 60% then smaller battery draw down faster down to 10-15% then batteries balance out untill dead

[@sotasolar]

Somebody is thinking this through, great comment!

[@OurBlackCatCottage]

I think it is going to fine..... hope I am right because I have several of capacities now. LOL