Save yourself some time and trouble and purchase the upper case that already includes the battery. That turns what is a 1/10 in repairability rating into a 9/10 repairability. There are repair/replacement guides here for all of the other internal bits, tricky or not. I’m more careful than quick, but it still took under three hours to swap everything over and re-assemble.
Replaced this and the front-facing camera. Apple had told me that given both front and back were out, that it was a board problem. Incorrect. I successfully replaced the front facing and rear facing camera, and then the flashlight started working again too. Great stuff.
Totally stuck the landing! Thanks for the great guide. One thing. Possible to use more colors in color coding screws? Before I started, I had read through the guide, but presumed I only had 3 different types of screws, when in reality, red and orange change throughout in terms of the length of the screws.