My battery has been randomly shooting down to 1% and my phone's performance had slowed down. I took advantage of the Ifixit sale on battery replacement kits.
The repair itself went very much according to the guide. The challenges that people noted in the comments in the guide were really helpful to know before I got started. The tools in the kit were incredibly helpful and I wouldn't have been as successful without them. I highly recommend the zip-tie around the phone as you pull up the screen because that security blanket really helped me keep control of what I was doing.
I did have some challenges. The 1st was that my adhesive strip under the battery broke when I was pulling it. I used the old video for pulling out the adhesive and may have been more successful pulling it straight out. I highly recommend heating the back of the phone for a bit to loosen the adhesive. The other challenge I had was reconnecting the home button cable. It is very small and you cannot have the phone very open to connect it back so it took a lot of patience but eventually I got it connected again.
Take your time. I suggest watching the video a few times before starting and also reading the guide and the comments. The heating tip to remove the adhesive is a must. If you do break the adhesive, not to worry, just go very slowly and try to grab the adhesive strip again, or if you must, slowly scrape and pull. This isn't something you can rush through especially if it is your 1st time.