5 - 30 minutos
I was having issues with my iPhone 4 holding a charge. I figured that it was most likely a bad battery.
After installation of the ifixit battery, my phone battery life is as good as new. Replacing the battery in these is really simple you you have some mechanical ability. It is just three screws and the battery connector. The most difficult part on my phone was getting the original battery out. It was glue in there pretty good and you have to be pretty gentle not to damage anything in the phone while prying it out.
I at first tried to save a few dollars and bought one from an seller in Asia. I installed that battery and the phone was even worse. The ifixit battery works perfectly. My phone is as good as new again. Don't try to save a few bucks, go with ifixit parts the first time.