ORIGINAL: CGRetired
I was looking over the other batteries in my collection and have one that looks puffy. It's going to the same demise.
FYI:
There was a MA article ( if I recall correctly ) not too long ago, where the author tried to get info about the gasses produced that cause the puffyness.
He resorted to having the gases measured, and found that the bloating is caused by relatively inert nitrogen.
Then he measured the effect on the batteries, battery life and output.
Because he could not get a good explanation from the battery vendors, as they were much too vague, he concluded that if you have a slightly puffed pack, you shouldn't worry about it... but erring on the side of caution, he advised doing otherwise for more severely puffed packs.