iPhone 4S Battery
This worked wonderfully for me!
My iPhone 4s battery was discharging very rapidly since I installed iOS 7. Although I'd read reports that it's a software problem with the latest iOS, the phone is over two years old.
This repair has greatly improved my phone's battery life. Before I replaced the battery, when the phone reached ~7%, it would shut off at any time, and I could only use it for about two hours. The battery can now deplete all the way to 1% and I have much more battery life. I'm very happy with the battery kit from iFixit; it's revitalized my phone.
The battery replacement isn't easy -- the screws are very small indeed. The "pressure contact" popped out when I disconnected the battery. I had to look at the high resolution iFixit image to understand its replacement. To replace, first attach the battery connection, and then slide the "pressure contact" beneath the top screw of the battery connection. Fine-nosed tweezers make this much easier than fingers.
It went very well for me. The pram was reset when I rebooted -- the clock needed to be reset and the wifi passwords were forgotten. But the trackpad works great! Thank you!