Help Getting hot and shutting off..

[jshultz78]

I've had my incredible for about a year now, love the phone, but here lately I've been having issues with it getting hot faster than usual, especially when it's plugged in and I'm using it. and once it hits about 100 degrees it'll shut off, reboot, shut off again and so on until I pull the battery and it cools a little. I've tried a factory reset with no help, Even with stock apps, just browsing the internet or using the phone for a little while it'll get hot and shut off. Is this signs of a bad battery? If so, where's the cheapest place to get a standard replacement battery for it?