Worked great! Unfortunately, my “will not boot” issue seems to be with the board and not the battery. Steps were easy; the longest part was prying the old battery off and inserting the new battery. But nothing complicated.
Thank you so much for the guide! For the longest while I listened to tech “gurus” talk about how Retinas are not upgradeable and everything is soldered on the board. But no one ever took it apart to find out lol. Finished this in <10min and it worked like a charm. Super simple.