20 - 30 minutos
This iPhone was my Dad's, and it was having the same problems as everybody, dies randomly and needs to me put on the charger only to show there is 3/4th of the battery left. He got tired of it after a month, and ordered an iPhone 4s, and told me I could have this one. (being a student I have little money) so looking online for 10 minutes I found the problem was what I thought and I ordered this battery kit.
The repair went great. The battery came in in the earliest estimated date (i used priority mail). The only slight problem was putting the logic board back in right. After a minute i got it right. But other than that I got it done in under 25 minutes.
The biggest time saver would be to take a huge strip of tape and take a guide (if you use it) and label every time you take out a screw, and put those numbers on the tape, so you can it it back faster.