This is what Apple does. They'll replace your battery for $79. Third parties will do it for a bit less. Doing it yourself requires a weird screwdriver and some

This is what Apple does. They'll replace your battery for $79. Third parties will do it for a bit less. Doing it yourself requires a weird screwdriver and some other tools, but isn't terribly hard, and you can get a kit with a new battery and all the required tools for $25.