20 - 30 minutos
My battery would work. I would charge my iPhone for hours and it would say 100% full but once I took the iPhone off of the charger and played a game the iPhone would just die.
The repair went great. iFixit.com had a great guide that made everything easy. the only hard part was getting the original battery out. The people in the guide made it look so easy but i had a hard time. I eventually got it out though.
Just be careful and make sure you follow the guide. if you do this you should be completely fine and your iPhone should be fixed in no time!