My Iphone would suddenly go dead, sometimes it wouldn't charge or when it did would take forever to charge. Charge would not last all that long. After searching for causes I determined it was either the IOS version (this an issue through 10.2, I have 10.3), the battery (some Iphone 6's had defective batteries), or some other issue. I decided to change the battery and see if that fixed the issue.
The kit arrived and was well organized and complete. There were, however, no directions. I realized later that I was supposed to go watch the video! I think a little (no, GIANT) sticker in or on the box somewhere that says "GO WATCH THE VIDEO, YOU IDIOT" would be a good addition. At any rate, I found a video on you tube that listed the steps and I used that. Went fine. I was able to complete the repair without removing the screen but that is not without risk -- if you're not careful I'm sure it would be easy to damage the ribbon cable.
1. The screws are teeny tiny things. I kept track of mine by sticking some clear tape over them and taping them to the box. If you dropped one of them, especially on a carpet, color it gone forever.
2. I did not remove the screen, although that is recommended. If you decide not to remove the screen, be very careful moving the unit around (you can get pretty vigorous when removing the battery from the glue) so that you do not damage the connecting ribbon cable.
3. I did not know what the two strips wrapped in plastic were. They are replacement glue strips. If I had watched the Ifixit video I probably would have known that. So I secured the battery in the case with another adhesive. Again, I should have watched the video.