My MBP 17 did the same thing - it's been getting really hot. I replaced the battery with OWC's higher beefier one. Interesting that the battery KEPT swelling after I took it off. No goo coming out but the packets inside are quite visible. The heat may taken it's toll though - it's running like snail snot today. Disk utility isn't helping. Apple had already replaced the first one at 1.5 years (out of warranty) for free. Kinda don't think they'd give me a second one.