I'm still looking for the chemical reason one swells and haven't seen a reference explaining it yet. It is a gas thats generated and what I've read says its generated both in charging and discharging. Obviously generated outside of 'normal' parameters since most don't swell when merely charging or discharging.

I've had my share - I left some stored at 50% charge and was gone for much longer than anticipated (out of the country on assignment), when I got back most had a puffed cell - every one was the cell on top as I had left them sitting. I even had a new, never used one puff.