5 - 30 minuten
My iPhone 4 Battery was not holding a charge. After 20 minutes the charge would go from 100% to about 65%...
The guide was very good. I was indeed the owner of a phone with 'extra glue' under the battery. Thanks for that warning. Only one other minor problem was that a piece near the battery connector appeared to be sticking up after removal. However, simply flattening it back down with the back of the phone and closing it worked fine.
Before screwing the bottom screws back in, go ahead and see if the phone powers on - this will save time in re-opening to adjust the battery connector if needed. Once power was clearly applied - I reinstalled the screws - holding the phone at an angle to be sure not to drop the screws into the phone's connection port.