20 - 30 Minuten
Had an old iphone 3gs around, battery would not hold charge. Looked up on the web, landed here and walla, now the phone has a new battery and holds the charge well for all my songs.
Easy, followed the guide and 20 minutes later, the phone was alive. Heart transplant gone successful.
Just a note, if the screen cannot be parted with the suction cup, use a fine screwdriver or blade to pry it a little from the metal frame.