So simple, even I can do it! iPhone 3GS battery replacement!
20 - 30 minutos
The 3GS would show it had full (or near full) battery but would just turn off whenever it felt like it. I assumed it was the battery.
Thanks to ifixit's simple guide and video the battery removal and install was a snap. Everything was exactly as they described and showed in the guides. It was near perfect with one exception...
Man, that old battery didn't want to come out. Almost broke the plastic tool that was included to help the install. I instead had to use a tiny flat screwdriver to help loosen the old battery.