Weird cell degradation

[pinkpanda3310]

Can anyone explain this -



The pack is a few years old, beaten and abused (by me) it used to be a 6s but one cell got punctured after skidding across the road. So it's been used as a 5s pack for a while. Now it has lost a lot of mah, has poor punch and I could see one of the cells was deformed so I unwrapped it to take a look. The cell at the bottom has general mild puffing but all the others are swollen at the positive end. The swollen bit is rock hard, just back from the swollen ends it feels rather normal. Plus one or more of the cells has a slow leak 'cause I can smell it.

Any theories as to what's going on?