10 - 30 мин.
The iPhone battery was showing signs of rapid discharge, and twice the phone shut down unexpectedly at about 40 percent charge. I ended up upgrading to a iPhone 5s and keeping the 4s as a music / photo device and a backup for my wife's iPhone 4s.
The repair went very well and was completed in about 30 minutes. The most difficult tasks were replacing the very small screws holding the battery connector and properly aligning ground clip. I had a good magnifying glass handy to check my work and that really helped.
Sit down at a good steady table with good light. Clear your work space. Be patient with the small parts. Keep good pressure on the small screw heads when extracting and replacing to prevent stripping of the screw head. Stay relaxed with some good music.