I broke the digitizer on my iPhone 6 and had been experiencing deteriorating battery performance for approximately 3 months prior to this event. So I figured if I was cracking it open, I might as well replace the battery too.
It went very well. The hardest part was that my old adhesive strips broke prior to proper removal of the battery. I ended up using a hair dryer and several older credit cards to work it out. It was not fun, and the old battery bent a lot, but I got it off with some patience.
1) It would be great to have some suggestions as to types of hard plastic cards we could use to pry out the battery. Credit cards were about the right size, but not rigid or thin enough to be truly helpful. To be honest, I thought the repair kit would have come with the stiff card shown in the replacement guide. I'd recommend you either include the stiff card as part of the repair kit or make it more visible on the purchasing screen that this card would be helpful.
2) I bent the old battery a lot. Given the warnings that were provided in the replacement guide, I was very worried that I was doing something wrong. I would have appreciated some guidance or
3) When replacing the adhesive strips, it was not readily apparent that the black strip between the small end that goes on top and the larger bottom part needs to go over the side of the battery. If I was regularly doing this, I would have figured it out implicitly, but as this was my first repair, I almost had to start over for missing this detail. Making that more obvious would have saved me some heartache.
4) The adhesive replacement guide implicitly assumes that second bullet of Step 8 is assumed. Having a picture with a call-out or a highlight would have been helpful.