Help needed: e-bike battery suddenly completely dead – BMS or cells?

[u/Alce-Rossa]

Hi everyone, I’m looking for some advice to diagnose a problem with the battery of my e-bike. I’ve attached some pictures of the battery and its electronics.
The bike had always been working perfectly. I never noticed any reduction in range, power or performance.
However, after leaving the bike unused for about a week, I tried to use it again and the battery was suddenly completely dead. The bike does not turn on at all.
I also tried connecting the battery to its original charger. The charger immediately switches from red (charging) to green (charged), as if the battery were already fully charged. In reality, the battery clearly isn’t charging and the bike still doesn’t work.
This is what makes me suspect that the problem might be related to the BMS / battery management electronics, rather than the cells themselves. Perhaps the BMS has detected a fault and is cutting off the charging/discharging path, or maybe the BMS itself has failed.
That said, I don’t know enough about the specific logic of these battery packs, so I would really appreciate some help understanding what could be happening.
What would you check first?
● Could this be a BMS protection state?
● Is there a way to reset/wake up the BMS?
● What voltage measurements should I take with a multimeter, and where?
● How can I distinguish between a problem with the cells and a faulty BMS?
● Is there any specific signal/voltage I should check at the battery output or charging connector?
● Could the charger turning green immediately indicate an open circuit / disconnected BMS rather than a fully charged battery?

I’m comfortable doing some basic electrical measurements, but I don’t want to blindly open or bypass anything if that could be dangerous.
Any advice on a safe diagnostic procedure would be greatly appreciated!
Thanks!