I had one of the early generation 17" MacBook pros that ended up with a swollen battery. And when I say swollen, I mean the case eventually split in two and was about 1/2" taller than it was originally.

Granted this happened because glue in the battery was compromised by excess heat because Steve Jobs preferred heat over the sound of a fan, but the machine never rebooted or shut down due to heat or decreased max voltage.