What causes them to swell? Is it just from general use? /. From lack of use? / Age?
There was another post just a while back, and the poor guy destroyed his drone when the swollen battery became detached due to the swelling.
Bit late for reply, but see your questions were overlooked.
Could be a lot of reasons, even a bad build.
But mostly it will be from bad battery management . . . running them down too low a % in flight, leaving charged 24/7 ready for flight, storing them in high temps, and yes flying hard in sports mode often especially when ambient temps are high will run batteries hot.
Heat is an enemy of all batteries, wet or dry.
Lipos do gradually degrade like any battery too, keep an eye on battery cell balances from time to time, like after flight before going home, pop them in one by one and just check cell %'s.
The M1P and MPP batteries (genuine) have that little recessed area in the back that allows for a little expansion when hot, which (if it does happen) generally goes down after flight and they've cooled.
The
M2P has no recessed back, so if they expand in flight, the can eject, think there've been quite a few threads in the crash section where this has happened.
