5 - 30 minutos
I replaced my battery because I had to charge it almost 3-4 times a day.
The tutorial on your website made it easy. With or without the video is self-explanitory.
If you don't already own a pair of the tools, purchase it! The tools makes it helpful to open the iPhone and remove the battery. Adhesive on the battery makes it kind of hard to pull off the phone. The plastic opening tools makes it easy to pry the battery off the phone.