My 5 year old iPhone 6 Plus started to have battery performance issues. The battery life itself was %57. It would suck down power like a countdown timer in seconds!
Repair went very good. Just dealing with the stubborn adhesive tape. Took a while with the blow dryer to get the old battery and tape off.
Use a blow dryer or heat gun to warm the back of the phone. It will make it easier to peel the battery out. Do not peel the new adhesive tape apart right away, as it can all stick together and make a mess! I should have pulled it back, stuck it in place and then peel the rest as I push it more into place.