I was having performance issues with the phone, sudden shutdowns at 40%, charging several times during the day- all symptoms of a failing battery.
I must admit disassembling an $800 dollar electronic device was a bit unnerving. Despite the performance issues I became so fearful that I reinserted the screws and put the phone down only to return 15 minutes later. I watched the video, read each step, and rewatched that portion of the video until I was sure I knew what to expect. In some instances tool angle used by the actor was crucial in removing connections. The adhesive, the right side adhesive closer to the middle of the phone proved to be the most difficult of all. The adhesive just would not go around the battery and broke short- leaving me with a tough decision. I used the battery calibration card to slide under the opposite side, pressed the case flat while I worked the battery up and out. Probably not recommended by iFixIt- but nothing was damaged. Install of the battery and assembly took minutes after that!
Watch the video. Read the step and watch that portion of the video! The angle the actor uses is instrumental in removing the connectors! Use a dark colored cloth or felt sheet to work on. Use an organizer or an ice cube tray to hold the different parts and different sized screws. Take your time with the adhesive strips. Warming up the phone probably wouldn’t hurt either with removing the strips.