Is there any way to change the battery of a PS3 controller? If so, where do I get a new one!? and how do I change it?
If you search Google for ps3 controller replacement battery you'll find plenty of places selling them online, including Amazon. They may carry them in Gamestop if you prefer brick&mortar stores.
As for how to replace it, here is a YouTube video demonstrating the process. Looks fairly straight-forward.
When I was searching for these things I found an old Joystiq article where a Sony rep says that Sony will replace PS3 controllers if/when they die. This article was written before the PS3 released though, so I don't know if they included that in their official terms of service or not.