question

simonhorro avatar image

mixing Life04 batteries 90ah and 100ah

i have two 90ah life04 batteries and want to add two 100ah in parallel to obtain 390ah is this ok to mix different ah life04 batteries

battery capacity
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2 Answers
Johannes Boonstra (Victron Energy Staff) avatar image

As there are differences in the cells (resistor wise) and electronics (for balancing for example) a mix/match is not a good idea. Mainly as there will be substantial unbalance.

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Thankyou will not mix as that i believe will cause long term damage

PetaJoule avatar image

Even cells of the same capacity are sometimes worse than a flea circus when you try to keep them in balance. (Or if you replace a bad cell with a new one... you have to take great care so this new cell does not get damaged by over or undervoltage).

That being said - and in full agreement with Johannes - there is actually one way to mix cells of various capacities. Provided you have the same amount of each capacity.

Say in your case you would have 8 pcs. 90Ah and 8 pcs. 100Ah => then you could form a 190Ah 24V battery bank by pairing 8 x [90+100] and putting these pairs in series. Of course

a) the 90Ah "as a group" and the 100Ah "as a group" would need to be of similar quality/age

b) without BMS still a no go, but the BMS could be used to monitor these virtual 190Ah cells.


So it almost looks like that is what you did want to do in the first place, although I do not understand the amounts. You say you have 2 + 2 cells? What I described, that's only (with keeping sanity) possible if you would build up a 6.4V system with 190Ah capacity.

Putting them as 4 cells in parallel... and getting just one cell would by the way give you 380Ah - not 390Ah - and would too be possible, but then you would have a 380Ah 3.2V "virtual cell".

Putting these 4 cells in series is an absolute no go, with or without BMS, they would sooner or later look like The Three Graces from Peter Paul Rubens.

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