10 - 30 minuten
My iPhone 4S wouldn't stay on unless it was plugged into the wall permanently. After jailbreaking, I was able to see that the battery had less that 450mAh left, so I decided to replace the battery! After my local shops didn't have any left, and my AppleCare warranty was up, I turned to iFixit, after having heard good reviews.
The repair was easy and simplistic. It really required no repair skills whatsoever. The repair kit came in a small plastic bag (not in the cardboard box they advertise on the website) with all the essential tools required for replacing the battery (and the battery itself!). The battery had been charged through 16 cycles already and is at 1390mAh/1430mAh, which is not bad. The liberation kit was a nice touch so you never have to take out the pentalobe screwdriver ever again!
Be careful when taking out and reattaching the battery. I was confused at first, and I thought that to reattach it you had to slide it onto the four connectors and then realize that it snaps directly down onto them. Use caution!