This may seem like a silly question with the obvious answer being 'any puffing is probably a sign to retire them to the bench'. But.. Alot of the shoots i go on are often for a month-6 weeks at a time with no chance of getting new batteries in. They are often in very hot countries meaning that the batteries usually puff a bit despite my best battery admin efforts! So given that i am on location with slightly puffy batteries with no chance of getting more in and many more filming days to go still, how puffy is too puffy?.. and are puffy batteries more likely to catastrophically fail or will they just have a decreased capacity? P.S. currently using 2x nano-techs 4S 5000mah.
Laurence good question and not an easy answer. A little softness likely not bad. Visibly swollen then be careful. Start a log where you track charge time, may put back in and Internal Resistance. Might help you have some empirical data to help track when they might be getting near end of life. I've had some that simply went fully charged to 3.6v per cell in 20-30 seconds of flying time. They were soft and had no other indication they were going bad. Worst case though I can't recall seeing anyone post about this on the various forums would be a catastrophic failure with fire.
Laurence: I second Gary's observation: very good question. I don't think anyone really knows the answer to the question. I have not seen any hard science that would answer the question of how puffy is too puffy? There is anecdotal evidence that (a) puffy batteries can keep working, (b) that should they leak the gas inside it combines with moisture in the air to produce hydrofluoric acid (which, on a scale of 0-10 of nastiness, is a 12). All such evidence seems to combine to produce four words: We do not know. Oh, and the phrase: "And if we're wrong, the battery will catch fire." It's informative to do a Google images search for: puffy lipo battery Be sure to qualify the search with "battery" otherwise "lipo" is used as an abbreviation for liposuction. Andy.