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Battery cells dying? Suddenly got 40.3v on 10s4p pack and it won’t charge anymore

Okay guys, I had my enertion 10s4p Samsung 25r pack since 2016 and properly done only 200-250 cycles?
Last year one day all of sudden it dropped its voltage from 100%, 42v to 94%,41.2v after it’s being fully charged. I thought it must because cells are getting old. It still got charged to 42v though!

Yesterday I finished a 20km ride and came home with 0% (maybe still had more then 32v, from now on I’ll use voltage instead of percentage, learnt a lesson). I put it on charge and it only charged to 40.3v which is 80% from this indicator. Okay, then I turned the board on, off, on, ran the motors used up some voltage and kept messing around and eventually the charger turned red again and charged the board up to 42v then I unplugged it, it dropped to 41.2v as expected just like what it did in the whole year.

Now, I just did a run again and charged it. This time it stays at 40.2v and I can’t trick the board/bms/charger again :sob:.

Question here, i know my pack is getting old but I really didn’t do that many cycle in the past, it’s just because the time so it doesn’t hold voltage? Isn’t charge rate being set by bms or charger? I don’t really know anything about building battery pack but how come it lost 1v of capacity in a run… did I wreck it or it’s just about time…

Any help/knowledge would be appreciated. Thinking of building a 10s10p pack for my sloppy kart.

Li ion cells lifespan can be as low as 300 cycles.
They age in time no matter the numbers. They can live shorter if you leave the pack fully charged for long periods. Your pack is dying very soon but not a one in a million case. Close to 4 years old is ok in my book.

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Always stayed at fully charged… I did left it at 60% for a winter two years ago but now it didnt help i guess lol.

Alright but what makes the charger to turn green at only 40v? BMS? Kinda know how it works…

Turns green if nothing is taking power. The cells simply won’t take more volts. Take a look at this:

Once you start using a pack just use it. It won’t last a decade anyway. They start dying beyond 5 years old used or not.

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Open it up, find the low P group and charge it. I can almost bet one P group is low.

One or more of the cells is probably dead (permanently low). One thing I learned: Don’t try and force a charge. If you can’t charge a cell like normal, its because the chemistry is different now and instead of charging the cell just gets hot.

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Donno how to do mate… put multimetre on it and everyone shows the same voltage…all in group, how do i measure individual cell?

Got it, thanks!

Uh anyone knows how to measure idnividual cell?

you have to take the p group apart to measure specific cells

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Could the BMS be bad? I’ve seen a BMS failure take out a perfectly good battery pack

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Well thanls guy after spend a whole night after work watching youtube and articles…now I’mm gonna go big make a 12s10p maybe even bigger by using Vruzend battery holder kit and just gonna ebay everything to home lol… lets having fun!!!

Battery pack size isn’t really a issue for me.

Sounds like this willbe your first battery.I suggest making something a bit smaller. Large packs are increasingly more dangerous. I have had 2 friends almost burn property to the ground with batteries

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Cool mate yeah ill upgrade to 218mm truck and sensored motors so lol budget exploded… smaller battery pack for sure!