At almost 3 years old, my iPhone 6 battery would only last a couple hours before needing a charge. Even less in cold weather. The phone is perfect otherwise, and I could not justify paying major $$ for a new phone if I could replace the battery.
After first watching the battery replacement video I powered down my iPhone and carefully followed each step on the phone. The quality and accuracy of the repair guide was very good, and I didn't encounter any surprises along the way. The included tools worked perfectly and were of a higher quality compared to tools that I've received in the past from other companies. For additional peace of mind, I also ordered the iSclack Opener, which easily and safely opened my phone, but after seeing how easily the phone opened you would probably do fine with the included suction cup. The adhesive strips came off without tearing (be patient), and I was able to easily apply the new adhesive strips to the new battery and reinstall. My phone was easy to reassemble and I performed a hard reset per the replacement guide. The phone powered on and I used it until the battery charge dropped below 10% then fully charged to 100% to calibrate it. The whole replacement process took about 40 minutes because I was taking my time and being cautious, but it was not very difficult at all for me. I am very pleased!
Watch the repair video both before and during the repair process so that you don't forget or skip any important info.
Work in a well lit area. My middle aged eyes also found a magnifying glass helpful!
Don't rush things—especially the adhesive strips. Be patient.