I had a bad cell in one of my zippy flightmax 5000mAh 6S packs, so I bought a 2S 5000mAh turnigy pack from ebay with the same C rating to repair it. When I opened up the pack with the bad cell it was obvious which one was bad, it had slightly ballooned (marked with black sharpie in photo).
As the cells in the pack are kind of glued together with strong double sided adhesive I decided to slice open the pouch and remove the insides, so avoid risking the two neighboring cells......not a good idea...as soon as I cut into it it flared up and went haywire, see video.
Fortunately it didn't damage the other cells, so I simply pulled the remains out and re-soldered the new cell in place. I will be doing some tests and re-balancing over the next few days to confirm it works ok.
I have one spare cell left, if I get another bad cell I can replace it, but a bit safer next time!!! these things stink when they go!!
(the vid will be added in a few mins, youtube is slow)http://www.youtube.com/v/U7n_ZSl256s&hl=en_US&fs=1&