48v 13s4p 18650 showing 0v for 12th cell group

Hello,

I am a novice e-biker and have only been riding for a couple months. My battery stopped working (would not charge and would not power on the bike) and the seller was non-responsive to my issue. So between buying a new battery or discovering why mine is borked, I figured I would investigate a bit further using the various videos and how-tos online. So I gradually disassembled the pack (after a plethora of charger and connection troubleshootings). Long story short, my connections are fine and the charger is fine.

I have found the following voltages via pinpointing on the BMS:
Group between cumulative
1 3.55 3.55
2 3.55 7.1
3 3.55 10.6
4 3.55 14.2
5 3.55 17.7
6 3.55 21.3
7 3.55 24.8
8 3.55 28.4
9 3.55 31.9
10 3.55 35.5
11 3.55 39
12 0 39
13 3.55 42.5
I take it from this that at least one and maybe all four cells within group 12 are dead. Or would a short somewhere also cause this? When I plug the battery to the charger, group 12 jumps to 5.85v and the cumulative at group 12 is 48.7v and at group 13 is 52.4v. As soon as I unplug, group 12 drops right back to 0v.

There is no physical damage to any part of the battery (it was never dropped or mishandled or anything) and it worked for a good month or so before just one day dying in the middle of a ride (the battery was probably around 70% charged at the time).

I do not have the spot welders or capability to take out the cells and put in new ones, plus I also don't know how to find matches for them... The battery is pretty intricate in design, it's one of the ones that goes in a metal case inside the top tube of the frame.

Thank you for any advice.

Group 12 is toast, cause could be bad cells, Bms faulty or sense wire connection failed.
Some pics of the battery cells, maybe someone can help out if your location is known.

Hello,

Please find attached photo. Hopefully it is of some help. The batteries are "inr18650-26e" I believe. Chinese obviously.

Thank you.

I'd load the 12 individually a few seconds or minutes to see what it does.
if that's all you got, maybe a 5v mobile phone charger. Careful not to exceed 4.2v.
So you can see that the bms isn't faulty.
load in a safe place to avoid fire.

Looks like they might be Samsung 26F/J series clone.
You can try the manual charge route but group 12 are not trustworthy and a liability, so be warned.
Any attempt should be done using low ma say no more then 400- 500ma charger out side and keep a very careful eye on the process. If they were around 2.8v then you have a good chance but going that low they are a weak link and will always be an issue, IR will likely be high.

See if you can measure directly on the cells on group 12, is it still 0 on all of them?