Wonderful but critical (Li ion cells)
Indeed, the fix was an overkill. But we must learn thoroughly the issue and kill the causes, not just the consequences.
Certainly something improved in the charging/management of the batteries. The failure rate shows. And the "container" was not necessary. Til this case:
Question: Undetected parameter (electrical and/or thermal and suddenly, smoke and spill?
This sound as an indication of cell abuse. Certailnly when charging the battery.
Very suspicious of additional "room for improvement"
I strongly suspect now:
1) Lack of per cell thermal monitoring
2) Lack of per cell voltage adequate "processing".
My experience with these cells shows they are much more critical than other chemistries. Abuse notably during charging is unacceptable. What kind of?
Not proper thermal and voltage in a "per cell" basis.