iPhone 4 battery was dying within a day, and I was too cheap to have someone else fix it.
The repair went pretty well. A couple of comments:
1. The plastic tools (see pic) were useless. They broke off immediately; both of them.
2. The two screwdrivers were absolutely necessary! My iPhone 4 had the 5-point Pentalobe screws.
3. When I removed the old battery the connector part broke off of the battery (see second pic). This was ok since I wasn't going to use it anyway.
4. I had trouble connecting the new battery to the iPhone. When I looked at the connector on the phone it seemed I had to slide the new part in from the side, but that didn't work.
1. Don't buy the plastic opening tools, they're too fragile.
2. Buy the screwdrivers; they're worth it.
3. When you attach the new battery connector to the iPhone, just push it into place (it'll "click"). You don't have to slide it in from the side. The video could spend a little more time on this step to show/explain it better.
4. The instructions advise replacing the tiny screws with new ones. What are the sizes of the screws (thread, diameter, length), and where can one get them?