5 - 30 minuten
I purchased a "broken" iPhone 4 on eBay with what sounded like a software issue. After restoring the system software, it worked, but kept suddenly dying, even when showing 80%+ power. I researched and found it was probably a battery issue. Indeed it was, it has worked perfectly since I replaced the battery.
The video and instructions were great and easy to follow. The kit had everything I needed. The battery connector cover was a little harder than I expected to pry loose, and I was worried about breaking something, but using the plastic pry bar and following the instructions, I got it done. I also had some difficulty getting the battery loose - it had something like double stick tape behind it. I pried around it, especially on the outer side, with the plastic pry bar. I'm pretty sure the tab would have ripped off if I had tried to pull hard enough to get it out that way. I had a problem getting the metal clip covering the antenna connector to stay put when reassembling, because I was forgetting to put the little screw back in! I couldn't plug the battery in with the battery in place, as instructed, so I removed the battery slightly, plugged it in, and slipped the battery back into place. It took me about 20 minutes from start to finish. I let the phone charge fully before using it with the new battery, and let it drain completely till it shut itself off the first day after. It has not given me a single problem since I did the replacement, about a week ago.
Be careful, but be a little firm if you need to be - just follow the instructions. (I only wish the instructions had gone step by step through reassembly - I would have been reminded to put the screw in the connector cover!) And if you have carpet be careful with those tiny screws!