20 - 30 minuten
After 3 years, my trusty 3GS' battery started acting up. I postponed any updates from iOS 4 to conserve battery life, but the original battery just ran out of juice. The phone started randomly rebooting, apps crashed and plainly stopped working during our recent ski trip - due to the cold weather.
Fairly easy. I am quite deliberate when it comes to fixing things, so it took me ~40mins to change out the battery. Followed instructions from YouTube. Included kit items came in handy, particularly the magnetized screwdriver - those screws are tiny. I did have to open it again since the WiFi connector (#6?) popped loose & I had to snap it back again, other than that it went flawlessly. After charging it, I upgraded to iOS 6 - I was pleasantly surprised that the battery life is very similar to my old battery (when it was new) even with iOS 6! Now it is like having a new iphone ! I'm set for another year of use before I get the next version (5s or 6 perhaps).
Follow instructions, take your time and be gentle. It is not as hard as you might imagine! One thing I did was to use a tape to hold the top end of the phone while pulling out the bottom end with the suction cup - this will help stop any accidental ripping of the connectors. If you have any extended warranties, I'd advise against DIY - I'm sure they won't touch it if the sticker inside (on top of one of the screws) is broken. Finally, after a few gambles, I try & stick with reputed sources to buy such replacement kits.