Easy 15 minutes, mainly waiting for my wife to lend a third hand
15 minuten - 1 uur
Battery started shutting the phone down at ~35%, especially when slightly cool, when starting the camera, and particularly at inopportune times such as an unexpected opportunity to climb a tower crane (no photos to share or prove it happened!)
Easy once I got a third hand; take out screws, pull on suction cup, insert opening tool on left or right side of screen bottom (needed third hand to place the tool) - there are easy grooves on either side in which to place the tool, but not the middle of the screen bottom.
With the screen released, I realized it would be easy to keep the 3 ribbon cables attached the whole time and save that hassle - took out two screws over battery connector, popped that off, heated the back of the phone with the halogen desk lamp I was working under for 30 seconds, pried carefully on the battery, it released quite easily, new battery was in and connected within another 2 minutes, all closed up and done in 15, which was mainly waiting for my wife to lend a third hand!
No need to use any other tools than those supplied - the key is to hold the case with one hand, put the suction cup as close to the home button as possible and pull on that with hand 2, then place the opening tool into one of the grooves that appear on either side of the base of the screen. There's nowhere to slip the tool in the middle, but either side has a spot perfectly suited for hand 3!
On the 3 ribbon cables:
I didn't bother removing them, just held the phone so they wouldn't be stressed (90 degrees) and had no trouble. It saved some time, and I didn't have to worry about the fragile cables or having the screen not work when reattached.
On removing the battery:
Heat. Just a little was fine, I just held it near a halogen desk lamp for 30 seconds and BAM, it popped out with minimal effort.
Some folks would be better off having 2 free hands to work on things and removing the 3 other ribbon cables, but this way I could have literally done the job in 4 minutes if I'd known these tips beforehand.