5 - 30 minutos
My battery in my iPhone 4 wouldn't charge so I thought I'd try replacing the battery.
Your guide was excellent and it was as easy as you made it look. I was a little disappointed that the Plastic Opening Tool that I ordered for the repair broke the first time I used it while trying to pry out the battery as you recommended. I probably put a little too much oomph behind my prying, but I was disappointed nonetheless.
It didn't fix my problem, but that wasn't your fault. Your guide was perfect.
Don't pry too hard if you are using the Plastic Opening Tool, it might break.