Bms drifting issue

Hi, need help diagnosing this. I found 1 pack of 12 unbalanced. After manually balancing and charging it I see that the same pack number 4 keeps loosing voltage. I’ve replaced with a new pack and the drift continues. Then I disconnected the bms ( bestech hcx-d223v1 ) and this pack keeps voltage perfectly. Everything points to a failure in the bms to me. I’ve checked all the wiring and it seems ok. Any thoughts?

BMS issue.

So there is something else to be done besides replacing it?

Unless you have some electronics training/knowledge it would be best to just replace it. Probably a failed transistor or resistor. Maybe a comparator. Chinese components have fairly high failure rates.

Without knowing any more, it would indicate a BMS issue. You can also manually inspect the BMS to see if a part is accidentally missing, but replacing it would be a good start.

how much of a drift?

So as your suggestions I’ve checked the bms and look this

IMG_4364 IMG_4366

It’s a focboxs bolt in the bms. So easily removed and I was so happy, I thought this was the end of it … but no. Now it won’t start AND keeps drifting pack 4 from 3.70v to 3.52 in a night.

It probably shorted out some of the components, I would toss that thing in the trash and get a charging only BMS from ebay.

I mean, I have a bestech as well, and they do seem to be great, but to get you back on the road, ebay could be a faster alternative.

I think I found the culprit. Makes sense way the pack number 4 was drifitng.


Although now the e-switch is the one not working, the bms it’s always on.