20 - 30 minutos
The charge from my original battery couldn't even make it half of a day, and it would randomly shut off when I opened applications. So I decided to give this website a try!
The repair was very simple, and went right along with the "Installing iPhone 3GS Battery" guide from this website.
Take your time when repairing your iPhone, you don't want to damage anything else! I found it really easy to draw the outline of the iPhone on a piece of paper and put the screws where I took them out of on the drawing.