Tl;Dr
As the battery rests in a deep discharge state, the electrolyte breaks down, turns into gas, and the battery poofs up.
I found this with my old PSP that I had stored away for years and pulled out one day for nostalgia purposes. Popped the battery cover off and it was all swollen like a balloon. It was quite a terrifying issue to have to deal with. Back in the old land of reddit, they even had a sub dedicated to this called r/spicypillows
Lol @ "spicy pillows" ๐
Spicy pillows
Special ravioli
It's just getting filled up with love.
And when they are ready to share the love - they do clearly, without mixed signals! <3
The battery auto-ejects as to make the replacement of said battery easier.
This used to happen with my drone batteries (because they are abused and I'll suck every remaining bit of charge out of them in a flight, and they don't contain a BMS circuit) until I learned to keep an eye on voltage and put them away with a "storage charge" and check on them every month or so. I'd stop the flight with some overhead to account for surges that may drop the voltage to below safe levels where before I'd run 'em until it almost fell out of the sky.
We had like six batteries for our (local firefighter department) drone, but always charging 2 to the may in case of an emergency. We already blew up one, three to follow. They are bloated a bit, but enough for them to get stuck in the drone often, and even a little bit is a lot for a rectangular battery. And they hold basically no charge anymore.
Don't do this, dangerous
When I was in school my phone battery expanded and would pop out of place. So I took the battery and put it on the floor and jumped on it to get it back into shape and put it back in my phone after.
I'm amazed it never exploded
Make a hole in it and you'll see.
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