🔋 Puffed
A swollen LiPo — a sign of damage or abuse (over-discharge, over-charge, heat, or a crash). Retire a puffed pack; don't charge or run it.
What it actually does
A puffed pack is one that has swollen because gas has formed inside the cells. It is the clearest visible sign that a LiPo has been damaged — by over-discharge, by heat, by being left at full charge, by physical impact, or simply by age. A puffed pack is finished.
In practice
Common causes are running the pack too low, charging or running it while hot, storing it fully charged for long periods, and crash damage. Sometimes a pack puffs slightly after one very hard run and settles; sometimes it stays swollen. Either way it has told you something.
Worth knowing
Do not charge, run or store a puffed pack. Take it out of service immediately, keep it somewhere non-flammable and away from anything that matters, and dispose of it properly at a battery recycling point.