My iPhone 6S, which already had been replaced by Apple 3 times, started to randomly shut off, not even turned on again, sometimes. It also could only hold a charge for about 2-3 hours, so since Apple said that I don't have warranty on that phone any more, I decided to replace the battery myself
Repair is pretty easy...for a person with a little experience. Though this was the first time I repaired my own phone and this wasn't cheap, I was a little nervous, but I made it, just left a few very deep marks in the frame, but that's not bad since it was damaged before anyway. These adhesive strips though, that's real pain, ripping them apart in the middle and then struggling to get them out and being scared to punvture the battery...In the end I made, and man am I happy now
Don't follow the guide as regards removing the adhesive strips...DON'T roll them around yur tweezers, that just rips them even faster.
When reapplying the adhesive Strips, watch out that they are alligned correctly, once misalligned there's no turning back