The OEM battery on my iPhone 6 was not sustaining the same battery life it once did. Following the recent Apple news indicating that older batteries with degraded performance cannot run the iPhone at peak operating conditions, I decided to just replace the battery. Battery Life app was showing that current capacity was only capable of around 80%.
I thought about bringing it to the Apple store to have them just replace the battery. But then I thought about the process of making an appointment, the wait, how long is it going to take....nope, I'll just do it myself. Glad, I did. The repair was easy. I didn't even need to fully disconnect the display. I just watched the video and followed the guide; step by step. Wasn't hard to replace, went smooth.
Removing the adhesive strips is the hardest part. Just make sure to first pull the tabs out straight, keep the tension firm and go slow. Make sure to read through user comments/advice before starting the repair to see where other people may have been tripped up on. Also, you may want to follow the battery calibration instructions. In my case, calibrating the battery after the initial installation seemed to be a good idea. Initial Battery Life test right after install was showing 92% capable capacity. After calibration, tests were showing 99%.