The battery would just shut off whenever it wanted, the percentage of charge would say 1%, I'd charge it for a minute, suddenly it's up at 70%.
I went into this like it was open heart surgery which is not good. I treated every part of the phone like it was a glass egg and can break if I breathed on it wrong. Also not good. Maybe these phones are more robust than I think though. Opening the case up was easier than expected using the one suction cup. I actually kept my phone in the case which acted as a good thing to hold the phone down on the desk while pulling up on the suction cup. I checked to make sure the screen would clear the edges of the case. I rested the screen at 90 degrees along the front of my imac screen while looking at the directions. Prying up the battery terminal was the first stumbling block. The tools sent were a little too wide to go in flush so I used the side of the prying tool to stick the little edge in. Then the strips. Ugh. They seemed to be coming off fine, I pulled them along the sides and then they just wouldn't budge anymore until ultimately broke. This is when I realized these strips were the embodiment of Apple clutching onto the battery not wanting me to do this on my own. After that I heated up the case with the hair dryer and used an ID card to pry up one side. It was slow going. I used the pry tool but saw I was denting the battery! I heated up the case again and then used the ID card and pushed it left and right. Kind of working it like sliding back and forth to open a locked door. Eventually I got to the point where I could pull the battery free with my hand. It was a big relief. I put the new battery in, debating whether to put the strips in which I did put on. Attaching the battery cable to the terminal was tricky. There's nothing I found on the guides that suggest how to snap it in place. But I'm sure people who have experience in electronics find that intuitive. I closed the case and screwed it shut and now all is well. I'm looking forward to see how it performs over the next few days.
I'd say take the screen off. There's alot of talk about skipping those steps but if you take it off it'll be easier to manage once the strips become a pain. I didn't do it because I was not confident I wouldn't break anything but next time, I'll do it. I wish I had better advice on the strips. Those seem to be the wild card and the heating may or may not work. Maybe the friction of my shimmying my ID card heated the glue as well and made them loosen their grip. In the end, it seems like the strips are so low tech to be part of such a high tech phone. Apple. Later I thought maybe I should have just cut the new strips so there's less surface area to deal with if I have to make the repair again. I doubt the battery needs that much tape to hold it securely. Edit: A day later, all is good. The battery holds a strong charge exactly like the original battery when new.