Although lipo is not supposed to self discharge, something is going on. I stored all of mine at 50% charge when I went out of the country thinking I would be gone for 3 weeks. I was gone for almost 3 months and everyone of them had puffed a cell (the one physically on the top) when I got back.

Regular useage seems to be teh best. This is an issue where a123s seem to have a real edge.