Smart BMS killed first cell

Sorry to double post on another thread, but no one seems to have any answers… I built a 12s3p pack with Samsung 25r cells with a LTT/Xiaoxiang 10-15s bms wired as a middle man for charge and discharge image I had my belt break and school was starting so I put it aside for a couple of months. one day I decided to check in on it to make sure everything was good… The first cell was at ~0.15v the second was at ~2.5v while the rest where at ~3.7v!

I tried to leave it plugged in for a couple of days to hopefully fix the issue but no luck. Maybe the bms takes parasitic power from just the first cell? I dont think the bms draws that much power but maybe I’m wrong? I have a video of the wiring, I could upload it if that would help with diagnosis. Thanks for the help!

Edit: The multimeter confirms most of these readings, however the first cell shows 5.7mv and the second shows 3.8v

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Has nobody gotten back to you as of yet? I am curious to this answer as well as I have four of the same smart UART BMS’s. The only reason that I can think of on why that one cell has been drained is most likely due to the fact that you had your board sitting aroundWith a broken belt and didn’t use the board for a while and at the same time was never disconnected using an anti-spark as well as 1 of those Xt90 to Xt90 (key) which Will prevent something from draining that first cell (which I would just replace). Also, make sure you store your board in room temperatureOr basically just making sure to not allow it to be in cold… such as a garage in the winter. Also, After reviewing You’re BMS’s wiring it seems like you are showing a positive and negative connection to each side of the cells. Maybe that’s just because you’re showing the red and black red and black red and black and I would like to see your build video… please

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Everything is disassembled right now as I’m repairing it. I’m pretty sure it’s just because I didn’t fully disconnect the pack from the BMS for storage, here are some pictures of when it was assembled

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I do that regularly on my Ebike. And have left it unused, for long periods. The battery stayed up. I used NOOOOOOOOOOOOOOOOOOOO BMS on that pack though. I guess they bleed a little.

They need to make a LION trickle maintainer. That acts like my hobby charger. If the battery cell is under, it charges it, if high, drains, to storage level.

Had same issue when baterry negative cable lost conection to B- on bms. Check this cable or even resolder it to be sure :wink:

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I only had something like this when my balance cables were shorted inside of the connector… but it was kind of different, still if you have not checked this yet, maybe it can help.

The cells and bms are completely apart and unsoldered right now but I’ll keep this in mind when I put it back together.

I’ve had the same experience as @Blix, I had a similar voltage reading when I had a broken balance wire. I’ve also left my BMS connected to my battery for 3+ months no use, without any change in the cell voltages

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