I have two family members whose phones were getting older. Their batteries didn’t last very long, and the iOS 11 software update really had them struggling to keep up.
I started with the iPhone SE, which in retrospect was probably the more difficult of the two, so if I had it to do over again, I would have done the iPhone 6 first, but overall it went pretty well. The only major mistake that I made was not reading the whole iPhone SE battery replacement guide before I started. I was just following along with the video, so I accidentally skipped the step to heat up the back of the phone before trying to pull the battery adhesive strips out on the iPhone SE. Needless to say, they broke straight away, and I ended up demolishing the battery trying to get it out after that, but I was careful not to damage the phone itself in the process. It wasn’t until I read through the iPhone 6 battery replacement guide that I saw the separate guide for adhesive strip removal, and I definitely wish I had seen that before I jacked the iPhone SE battery all up, but oh well. In the end, I was able to get it all put back together with the new battery inside, and everything worked perfectly. After that I did a lot better job of reading through the whole iPhone 6 battery replacement guide before I started which helped that repair go much more smoothly. Thanks to the experience from doing the SE and actually following the written guide instead of just the video, I was able to get the iPhone 6 battery replaced in under 40 minutes with zero issues.
Read the written guide all the way through before you start. Read/watch the adhesive strip removal guide before you start too. I found that heating the back of the iPhone 6 up with a hair dryer until the aluminum was warm in my hand helped the adhesive strips not to break when I pulled them out.