How can I tell if a Lipoly cell is bad?

Hey, so I've had these Maxamps 5s 4000mah packs for awhile (only ran each one once though, and due to a LVC screwup, both packs puffed). I just disassembled the packs and one cell in each of the packs is a bit softer than the others, but none are puffed. (my balancers also showed that only 4 cells were in balance, so one had to be off). Each pack has been fully charged since the puffing (but not run), and they've maintained their voltage. So my question is... how do I tell if a lipo cell is bad? I've been thinking of charging each cell separately, but want to make sure that will help me come to conclusions first. Thanks!