10 - 30 minuten
For months, my iPhone 4S battery had not been holding a charge for more than a few hours. It got so bad a few weeks ago that I would take it off the charger and have 100% charge and within a couple of hours--with only normal use and no extra apps running--the battery would be completely dead.
After reading reviews and doing a little research on replacement batteries for iPhones, I ordered a replacement battery kit from ifixit. Received the kit in a few days (I paid extra for express shipping) and life is great! The replacement took all of about 10 minutes (only because I got interrupted a few times) and now my phone works great and has much longer battery life.
Make sure you follow directions and don't get frustrated by any glitches. The adhesive on the original battery in my iPhone was a bit stubborn so I used the plastic pry tool included with the kit to loosen it up a bit. Once that happened, I pulled carefully but forcefully on the plastic tab and the battery came lose. Definitely watch a video--ifixit has a number of good videos available on YouTube--or find ifixit's instructions with images. It will make your life much easier.