Can I use different Ah batteries in a bank?

[jesfl]

I sought an answer a couple of days ago at the end of a long thread about my solar system (batteries/BMS) failure.

Can I use one new 12V 100Ah LiFePo4 battery with my existing (3) 150Ah batteries . . . if I can repair those 3 batteries with new BMS units (wishful thinking)?

A "no" pretty much means I would be wasting $700-800, or more. to "get by" for a month or two buying a new battery.

I searched a lot on the Forum. I found several discussions that seem to indicate using different Ah-size batters in a bank is possible. But honestly, the technical references and other uncommon terminology lost me before I could find a simple definitive answer of "yes" or "no"? (Or, find qualifying parameters that would lead me to a decision.)

I'm desperate because I've been without batteries boondocking for many weeks and my tolerance is exhausted. (Bought a cheap Walmart SLA for overnight power for alarms, fridge, etc.) Use solar for things when there is sunshine, but I do not have microwave and other appliances.

I am about to order a single 12V 100Ah LiFePO4 battery to try to muddle by for a month or two.

I am just looking for a "yes," it can be done, or a "no," not possible.

If yes, I'll buy a better quality 100Ah battery.

If no, I'll go as cheap as I can and, sorrowfully, consider it a throwaway.

Or, should I only consider buying a 150Ah battery so I can be used in a bank, if my dead 150Ah batteries are repairable?

I will appreciate any guidance,

Thank you, again.

Jim S.

 

[time2roll]

Yes as long as the battery packs are in parallel. No issues.

Series to make 24+ volts is trouble.

 

[Bud Martin]

I have been running my two DIY battery banks (each one with its own BMS), one is 90Ah (first built), another one is 280Ah (second built), for about 3 months now, no problem that I can see so far, I charge and discharge about 3200 ~ 3400Wh every day. I am saving money to build another 280Ah pack.

Parallel LiFePO4 12V 90Ah pack with 12V 280Ah pack, any issue?

In the November I built LiFePO4 12V 90Ah (Liitikola) pack with 100A BMS, now I also built 12V 280Ah (LISHEN) pack with 100A BMS (same model as used in the 90Ah pack). So does any one ever try this setup (parallel two different Ah battery packs) and see any problem in long term? My max draw at...

diysolarforum.com

 

[jesfl]

Thanks to both of you. That is exactly what I needed to know. I will order a 100Ah lithium battery this morning.

What I could not find mention of anywhere was whether different Ah batteries cause any solar or other charging problems?

Bud, in your case, do I understand that you have two separated, different-Ah-sized banks (90Ah & 280Ah) with those banks then connected parallel? Is that how it works?

Your quick responses are very much appreciated.

Jim S.

 

[Bud Martin]

Thanks to both of you. That is exactly what I needed to know. I will order a 100Ah lithium battery this morning.

What I could not find mention of anywhere was whether different Ah batteries cause any solar or other charging problems?

Bud, in your case, do I understand that you have two separated, different-Ah-sized banks (90Ah & 280Ah) with those banks then connected parallel? Is that how it works?

Your quick responses are very much appreciated.

Jim S.

Yes, I built 2 battery packs, each one with its own BMS, the packs are connected in parallel.

 

[Johnjayjrv]

Just curious what the Ah would be with the 2 different batteries. I'm assuming the saying still is true that the 2 in parallel Ah are added together?

 

[rickst29]

Just curious what the Ah would be with the 2 different batteries. I'm assuming the saying still is true that the 2 in parallel Ah are added together?

Yes, the Ah values are additive. The one concern with batteries in parallel is: the battery connections must be carefully balanced (in resistance), or you will tend pull from the "nearest" battery when you are running a high-current device. But that issue is not directly tied to the Ah, it's already present with your 3 current 150Ah batteries.