2 year old phones needed new batteries
Updated, cannot recommend this fix, see below.
Repair went well. I didn't need to disconnect the screen and used two rubber bands to rest the screen onto the original apple box. Of course the sticky tape was a small problem. One came out good, but the other one broke underneath. Used a hair dryer and a credit card to carefully pry the battery out.
One of the batteries was about 12% charged and the OS came up just fine. The other battery was below 1% and all that came up on the screen was the apple logo. I had to plug in a charger to get the OS to boot.
Smaller fingers may help in removing the sticky tape. When snapping the case back together, be sure to align the top tabs first then work your way down and continue snapping the tabs together.
Need to update this comment. The first battery was a no go as the connector part is to large and when the screen is pressed on it, the connectors get displaced causing the phone to lose power. I tried this countless times to bend the connector, etc. So I ended up putting my old apple battery back in. The ifixit batter sat on a shelf and now it has bubbled up on it's own.
The second battery went in better, but after 6 months, it is now dead. I can no longer recommend this fix. Just let apple do the replacement.