Series batteries with different AH

[EVTodd]

I know it's not a good idea to mix batteries with different AH ratings in series but is it ok if it's a small difference?

I have two sla 12v 7ah batteries wired in series for 24 volts and just added a third (for 36 volts) that is 7.2 ah. Is that .2 ah difference going to hurt anything?

 

[Link]

Mmm, if it's SLA, yes. If it's not, then you "might" be okay if you never reach the end of one batteries capacity.

If you really want to do this, just get two cheap 12V chargers and wire them up to each battery. This will keep them balanced. You should be okay as long as you never drain the batteries to their cutoff point.

 

[Rassy]

I'm not sure, but I think Link meant to say no (if it's SLA) it won't make a difference. SLA batteries often are a little different in their AH. If you follow the posts on LiFePO4, you see where the batteries AH increases when they are first cycled. So I don't think you have a problem regardless of the chemistry involved. Of course any battery is subject to damage if it is abused.

 

[vanilla ice]

I have done this and it will work fine. It really doesn't matter but you wont be able to fully discharge the larger cell. Non issue if you charge each 12v battery individually.

 

[Link]

Yeah, I wouldn't try this with a more expensive chemistry. Too risky. :? SLA can sort of self-balance.

 

[EVTodd]

Good deal... I got a brand new 7.2 ah battery from a friend for free (from a broken UPS) and was really hoping to use it.

Actually, I thought it was kind of strange that someone makes a 7.2 ah battery. Why not simply make it 7 ah?

 

[Link]

Actually, I thought it was kind of strange that someone makes a 7.2 ah battery. Why not simply make it 7 ah?

Marketing. Why buy a 7Ah when you can have a 7.2Ah for the same price? Though we all know rated capacity means virtually nothing.