I have a problem with my 3 year old MacBook. The battery has "swollen up" (I could post a picture if that is of help).
One side of the battery is much bigger than the other. Since it no longer works, I opened it. Inside it is 6 cells covered in metal envelopes. 2 of the 6 cells are about twice as big as they ought to be.
What do Apple's batteries contain? What could be the reason for battery cells to swell up?