My iPhone 4s had been living happily inside its Mophie protective case for years, until one day I noticed that the Mophie case had split open. I took the phone out to see what was going on, and discovered that the battery had swollen and ruptured the case of the iPhone. Yikes!
I live on a tropical island in Panama 35 miles from civilization, and that phone is my lifeline to the rest of the world. Just taking the phone back to the city to get it repaired is a $100 round-trip, plus a couple of nights in a hotel. So doing the repair myself was worth the attempt. My son was coming for a Christmas visit, so I ordered the battery and had it shipped to him. It arrived the night before he left, and two days later, here it was on the island.
I watched the Youtube video, and everything looked very straight forward. The replacement only took 5 minutes, and a little super-glue to re-attach the glass panel back to the frame and I was done. Very easy!
Make sure you have good bright lighting and a clean work surface. Those screws are tiny and if one gets away from you, you will never find it! Fortunately, the screwdriver tips (on the better quality screwdrivers) are magnetized, so they will help keep the screws from vanishing. The box iFixit sends their parts in makes a great holder for the screws as you remove them. Be sure to watch the video, as it shows how the connector cable disconnects from the phone, and how to pry the old battery out. If you pry at the wrong spot or in the wrong direction, you could break the connector, so seeing it done on the video removes that chance.