You made a little girl and her mommy very happy...
20 - 30 minutos
My old iPhone 3GS is owned by my little daughter (8 yrs old) - she uses it as iPod touch, loves to play games and music. The last few month the battery lasted about half an hour, a big annoyance because now it was stuck at home.
Although it was the very first time I opened an iPhone it went smooth from the begin till the end. Heads up for a perfect tutorial, except for one little detail: For European iPhones the step 6 isn't detailed enough (see Enlightenment)
Step 6 for European iPhones:
the connector 3 is easy to slide out (just pull) but very hard to put back. It took me half an hour to make the battery replacement:
20 for the #3 connector and 10 Minutes to do everything else.
The trick is that you need to hold the upper case in a 90 degree angle and then firmly push the cable into the socket. Be careful not to crumble it. Take a hot chocolate or glass of wine (this sure helped me staying calm ;))
iPhone 3GS Replacement Battery
Phillips #00 Screwdriver