how to find out which cell is dead...

Hey all. I think I have a dead cell in one of my packs. I have a 12s4p 30Q battery. I was having much more noticeable voltage drop when I rode my board last - certain hills that I had been able to get up without any issue were now not possible - the board was slowing down a lot more. I didn’t have time to look at it, so I took the overall voltage down to what I thought was a reasonable storage charge of 4.07. I’ve now had a chance to look at it (disassembled) and all the packs were at 4.07 still. Then I started the board and ran it a bit and tested each pack - the one pack dropped immediately to 3.8. I’ve now removed this pack and want to figure out which cell of the 4 is the problem, but I don’t know how. Can anyone advise please?

Charge each cell in a charger and see if one has significantly less capacity?

Not sure where you read that but thats way too high for storage, I’d say 3.5 per group. Maximum, minimum 3.3

It may take a few cycles for the pack to be back in good shape if in storage long.
If you have 4 cells ready to evaluate and all of them have the same voltage. You can either put a load across each cell to see of any of them sags exceltionally much(I sudgest 1-2C as a start). Or discharge/charge to see if they differ alot in capacity/IR.

Thanks @linsus. I did a capacity test after checking the voltage and the one cell was FAR below the others, so I’m assuming that it’s the problem.

Re the storage amount - thanks for the advice. I can’t think why I thought that was a reasonable amount…

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Sounds like you found the culprit :slight_smile: good luck!

Im in the process of rebuilding that pack - just need a decent soldering iron! Frustrating when my tools break!