5 - 30 minutes
My iPhone 4 was getting a bit old and the battery life wasn't ideal at all. I was charging it 3-4 times a day, which isn't very convenient!
Was so easy to replace the battery myself and it works perfect! My phone lasts for 2 days now!
I recommend ifixit products to everyone! Definitely gonna keep these guys in mind for anything else I might need in the future.