5 - 30 minutos
I pre-ordered my iPhone 4 (AT&T) and had it 1 day before the "official" release. Initially I would get almost 4 days worth of use on a full charge. After a few months, it dwindled down to 3 days...pretty reasonable in my book. I am pretty regimented on making sure I drain my battery all the way down, and then let it do a full charge (8+ hours) overnight using a wall outlet to make sure I'm keeping my battery at it's best-possible health. Recently my phone dropped to 2 days on a charge. It did seem to coincide with iOS 5, but I also knew it was about time for the battery to start fading. Debating on whether or not to upgrade to the 4S, I decided to hold off and wait for the next iPhone. In order to keep this a plausible decision, I opted to look into replacing my battery. If the solution was simple and relatively cheap, then that would be the direction I would go.
The repair went as simple as the video demonstrated. I have not had my iPhone looked at by the Apple Store, so I didn't have to worry about the special screwdriver,...just the standard #00 Phillips. About 5 minutes after starting, I had the new battery in and was letting it charge. I'm at the end of my 2nd charge now, and battery life is looking good... getting back to 3 full days. I'm going to have to give it a few rounds more to let the battery settle down, but for $30, this was certainly cheaper than potentially wasting an upgrade for the sake of battery.
Stick to the instructions/video tutorial - it made it extremely simple. Follow it to the letter, and make sure to clean the metal-to-metal contacts to ensure maintaining your signal strength.