it literally went from 36% to 92% in half an hour.
it charges super slow at times (i.e. stuck at the same percentage for hours) and super fast like this at times.
my tablet is only 2 years old. what is happening?
You can't fix a failing battery -- you can only replace it. If it's getting unusually hot while charging, then there's a potential risk for fire or explosion, so it's not something to completely ignore. Bring it to a repair shop.