LIPOs lost punch

[Catch 22]

I have 2 track power lipos for my LRP Shark that i hadnt used for a year . I went to revive them last week . One was fine and one had puffed up. the one that looked fine i charged it up and it is good as new.

I threw the puffed up one in a bucket of snow outside ....next morning it wasnt puffed up anymore. Its half down a bucket of sand at the moment