My last Apple battery on this very machine had a little explosion. When I got to the machine in the morning after it was on charge over night I noticed that the trackpad had come out of the top of the palm rest... I was a bit shocked.
On investigation a noticed the battery had expanded so much that it had blown the trackpad out of position.
Anyway, I removed the battery and remarkably the machine works fine now as long as its plugged in. I need something portable so I have just gone and bought a new machine instead of messing with repairs but it just shows be careful, if an official Apple battery can do that what could a cheap Chinese one do under the wrong conditions.