Mixing LFP batteries?

[soopad00pa]

Boat I'm this close to buying has a single 12v,100ah battleborn lithium house battery about 9mos old. I'm gonna need more juice, but I'd prefer not to buy more BBs nor give that one up.

Can I get away with adding another couple 12v,100ah or even a 12v, 200ah LFP without causing problems? Currently looking at renogy as I've had success with their stuff in the past.

Main draws will be a wheel pilot and refrigeration.

Thanks

[Statistical]

It isn't ideal to mix batteries of different brand, capacity, and age. It will work but there could be uneven and premature aging.

[soopad00pa]

So matching as closely as possible (skip the 200ah capacity and go 2x100ah) will make the best of a suboptimal situation?

My understanding is it's best to run unmatched batts parallel, but if specs (voltage, charging, chemistry, etc) match, then does should work, yeah?

[hlev00]

Assuming these are internal BMSs, the risk is that they will never be balanced thus ruining one or the other. I believe you can use your charger to get them both up to what they each think is balanced individually, but even then, with different BMSs they may target different charge levels leaving you screwed once again.

[Statistical]

Originally Posted by soopad00pa

So matching as closely as possible (skip the 200ah capacity and go 2x100ah) will make the best of a suboptimal situation?

My understanding is it's best to run unmatched batts parallel, but if specs (voltage, charging, chemistry, etc) match, then does should work, yeah?

Yeah I would go with 2x100Ah over 1x200Ah in this usage. One thing to look for but not all OEMs list is the internal resistance. Ideally all 3 batteries would have very similar internal resistance.

Simplistically we say if you have a 30A load and 3 batteries in parallel each battery will push 10A. However that is only if the resistance is the same. The load though each battery will vary inversely by resistance. The battery the most heavily loaded will discharge faster and reach LVD soonest. It will also be subject to more full charge cycle equivalents and have a shorter life. So ideally the batteries would all have as close to the same internal resistance as possible. A 200 Ah battery almost certainly won't.

I think if you can find two 100Ah batteries that each have close to the internal resistance of the original it should be ok given the old one is only 9 months old. If it was 6 years old I would say just sell it and start fresh.

[soopad00pa]

That jibes with what I'm seeing at DIYSolar too, I think. Thanks.

If they're this close, do you think series will be a problem?

[tanglewood]

I think my first choice would be to expand or replace with same-kind batteries. Based on owner reports, Renogy would be at the bottom of the list - actually not on the list at all - but that's a different topic.


Otherwise I'd just parallel them regardless of capacity. But they must all be LFP, which I think is your plan anyway. I think the only issue is how the different BMSes might impact each other in terms of resistance, when they balance, disconnect thresholds, etc. But I don't think there is really any practical way to assess all that since most are black boxes. It's sub-optimal, but how sub-optimal is all guesswork.

[soopad00pa]

Huh, renogy doing that badly? I'll have to dig around a bit. I've been using their stuff (not batteries admittedly) for years and it's been dandy. I'm sure DIYSP will have a list of the cool kid batteries.

Seems like parallel is what everyone's recommending - I've just only built in series before.

Thanks guys!

[Avionics_Joe]

I would repurpose that battery as the engine start battery and get a new house bank.

Joe

[soopad00pa]

Originally Posted by Avionics_Joe

I would repurpose that battery as the engine start battery and get a new house bank.

Joe

Interesting idea. I feel like I read somewhere that the lifepos often don't have the necessary cracking amps to be good start batteries tho 🤔

Is that a thing?

[Avionics_Joe]

I have a 4 X 4 of CALB 180 amp hour battery's, so my max discharge rate is 360 amps times 4 or 1440 amps.
You have to check the battery's specification to be sure, also the BMS might limit the max current.

[CarlF]

Just spend a little extra money for Battleborn. Drop-in Lithium batteries are not all the same. Battleborn is one of the best.

Whether it would work to mix brands, it will almost certainly void the 10 year warranty on your current Battleborn. And Battleborn has a great reputation for support and warranty. You can actually reach a knowledgeable rep on the phone.

And be sure to follow Battleborns installation advice. You may need to increase the cable size and change the fusing to safely handle the extra power you are putting in. If you ever have an insurance claim, your insurance company will deny the claim if they find the installation is subpar.

I doubt a Battleborn can be used for cranking. Few lithium batteries are designed for that and the BMS will shut down off you try.