5 - 30 minuten
Old worn out battery - phone would shut off if phone call started and phone was not plugged into power source - battery 3+ years old.
Replacement battery and kit was great, used 5 point screw driver to easily pull out old screws, and install new Philips screws when finished. I thought I would need a different Philips screw driver to remove the battery terminal, but provided screw driver worked great. Now we hope to get more time out of this iPhone 4.
Pulling battery out due to adhesive was the trickiest part, but careful prying on right side (right side when looking at back of phone - away from the circuits) using the phone frame as a fulcrum, using the provided plastic pry bar worked great.
Key was being patient, as if you put some pressure on the battery with the pry bar, you can feel the adhesive slowly give way. Once I had the right side of the battery up enough to grab with my fingers, slowly pulling on the battery (again feeling the adhesive give way gradually) got the battery out.