dangers of mixed different brand/age SLA in series/parallel?

N

needWheels

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May 27, 2008
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For anyone who didn't follow my recent ebay drama,
I've been stuck with various brand name SLAs of various age (2005-2006 or older)
Some charge to just barely 13 volts, some to 12.5 or so, nothing higher.

I'm hoping I can at least get a few cycles out of these before they become completely useless.

How dangerous is it to mix a bunch of different SLA with different drain rates in series and parallel?
What will happen in a worst-case scenario?

I was thinking 12x3 for short hops (they are 7ah) and 12x3x2 to attempt longer trips.

Thanks for any advice!
 
You can put any combination of batteries in parallel as long as the voltages match.

In series, it's best to try to match the capacity of each series unit.

Worst case scenerio (other than misconnection), is the thing dies sooner than expected.
 
Yeah, I wouldn't veiw it as hazardous, since you are using all same chemistry batteries. But the pack will conk when the weakest battery does.
 
I tend to lean toward running multiple battery packs one at a time, though it means stopping to switch the plug. It gives you some idea of how much you have used, once you know what to expect out of each pack. My bike has no dashboard. It also gives you the option of not carrying all the batterys for short trips.
 
I had thought of that as an option but it also occurred to me that since these batteries are known to be old/weak from the start, in parallel might give it some protection from deep hill-cranking loads.

I guess I'll have to do by trial and error.
I might not even get very far as it is and have to get fresh batteries right away.
But thanks for confirming that it's at least safe to experiment.
 
I've done it, 2p 7ah bats in series with 12ah 1p bats. Mixed brands. May not squeeze everything out of the stronger ones in the series, but works fine. I charged individually.
 
:arrow: A good trick...

If you are charging in parallel what you do is charge all of them together at first until they are all full. Then stop and disconnect the one's that are truly full by testing them one at a time with your charger. Some will still have room left and this top off charge will mean you get your full capacity.

If you stop when the weakest cells says it's time to stop charging then the strongest one's never get full.

I've got old and new mixed together and this is what I do.
 
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