Hi, a friend’s dropped off his board for a service / hoping for me to sort it out. It has a 10s4p pack of Samsung 30Q cells and its only measuring 20v for the entire pack (2v per cell). Is it salvageable / worth rescuing? Thx
Nope. They are ruined.
Even if they measure fine capacity or charge retention wise.
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If a pack is at such a low voltage (below 25V, average of 2.5V/cell) then the odds are good that the cells are all at very different voltages, some of which are low enough to possibly damage the cells. Even zero volts.
If all the cells were all confirmed to be at 2.0V and only for a short period of time then the pack might be recoverable. But since the cells are all at different voltages and have been at a low voltage long enough for them to possibly have been damaged, it’s best to not charge the pack and to just replace it.
If the cells are damaged there is a chance one or more could catch fire when recharged.
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Ok. So I’ve dismantled the pack and half are toast (zero voltage) the other 20 cells are at 4.03 volts .
I know you’re not supposed to mix batteries but I was thinking of getting some 2017 30Q’s from Nkon and making a new pack. These cells have probably only been charged like 30 times. Thoughts ? Thx
If you are trying to save money this won’t work, the extra tools and testing needed to mix cells has a long payoff.
Best bet would be to get all new cells - building with used cells (for eskate and low pgroup count packs) is lots more work to do well and much more likely not actually work or break very quickly if you don’t invest a crap ton more time and effort and money.
I really need to finish my article on reusing cells lol, linking it would be so much faster 
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I suppose I could make a travel pack 10s2p with the cells that are left
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Absolutely great idea, imho small pgroup packs are harder than larger batteries to keep balanced and healthy just because the small differences in internal resistance due to aging and cycle life don’t have as many cells to average out over.
So if the pack cycles without sufficient time to balance between uses it can get out of wack quickly - what i do is use a cheap llt smart bms so i can keep an eye on it and get more from the cells second life. I would highly recommend a dedicated internal resistance tester for matching the cells - the ir results from the smart chargers is absolutely unusable and often so inaccurate that it indicates trashing good cells and keeping bad ones
You inspired me finally finish my write up of my cell reuse process so thanks. Maybe something will be helpful : How to use old Cells successfully without burning down your house
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