Repairing battery pack


My 2 year old board broke down after the last rain, and water got inside the battery pack. The total voltage read 24v in the end, down from 42v for the full normal. I’ve disassembled it later, there was quite a bit of corrosion. I disconnected the battery from the BMS. I’d like to repair and repackage the battery, I’m trying to figure out what to do next.

  1. The pack is glued pretty tightly together. How can I disassemble it safely?
  2. The battery was 10s3p made of inr18650-30q cells. Could a 13s BMS work with a 10s config, leaving a few wires unconnected?
  3. Some cells read 3v, others <1v. Are those usable?
  4. I have more new cells, can I combine them with used ones in the same pack?

I’d appreciate any tips and advice, thanks!

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That pack is a fire hazard. 100% of that nickel strip would need to be removed and whats left would need to be VERY carefully cleaned up.

And here comes the dangerous part. Most of an 18650 metal shell is the negative connection, leaving only the center part of the cap as the positive. So besides the barley paper the only thing protecting from a dead short if something metal touches both is that thin plastic shrink wrap on the individual cells.

Discharging any li-ion cell below 1v will cause damage. You could have increased internal resistance or decreased cell capacity making it difficult to keep the pack balanced. Replacing those cells that were discharged to below 1v would still leave you with a mix of older and newer cells.

Couldnt tell you about that BMS and whether it would work at 10s. Look for data sheets and try to find the manufacturers website for more info.

Good luck and keep that pack somewhere where the smoke wont cause harm to pets/humans/property should the worst case scenario happen. At the very least get a lipo safe bag and store it in a metal container in a garage or something.

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Hey, thank you for your expertise! I have an update.

I’ve been able to peel off those strips. Turns out positive poles have a hard plastic circle around them, below the paper and the pink wrap. That made the process less scary.

I was thinking about the new cells. I could parallel them as 3, while the old ones, those that remain usable, could be batched as 4 or 5 in parallel. That would ease load on each of them and boost their aging capacity.

I’m not sure how to separate the pack in the middle and what to do with this glue. I think I’ll use a thin piece of plastic.

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Oh man, that is soooo dangerous. If you have just 2 cells connected in series and the plastic shrink wrap inbetween them is compromised you could end up with a dead short and a possible battery fire.

Are you sure you dont just wanna toss the entire pack into a bucket of salt water and leave it for like 3 months straight?

Every single shrink wrapper thats been damaged will need to be replaced. And maybe if you insist on recycling some of those cells you could reuse the plastic rings you mentioned.

Feebay has both barley paper sheets and barley paper insulator rings. As do other battery vendors that dont use feebay of course.

Keep in mind that no matter how you parallel or series connect older and newer cells, the older cells will run out of charge first then the whole pack will need to be charged.

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I would highly recommend a new battery if you don’t have the experience or knowledge building or servicing batteries. I do have said experience and that thing looks like a nightmare. New cells don’t cost that much and as mentioned above mixing old and new isn’t good.


Sorry for ghosting. I kind of went into one of those rabbit-hole-type dives researching this.

I’d like to build this battery myself. It’s not about cost, but more about understanding — about li-ion and electronics in general. Besides, if I get a new one, I might just drown it again in snow, there’d be no progress. Whereas building one would leave me details of its limits.

I’ve ordered supplies from china, it’ll take potentially months to arrive, not that I’m in a hurry. My current plan is to sort the cells — I wonder how years affected their capacity, compare them to the unused ones, how they sag under load, will grouping them into 4 offset that, how will they drift as they cycle, can bms compensate for that, how much current the motors draw. Anyway, this feels like a beginning :slight_smile:


Science is fun… be careful though… batteries can be extremely dangerous in the wrong hands. You seem to have done at least a little due diligence. Have you bought a welder?

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