I didn’t realize that each of the photos contained different steps until later on, (the photos look very similar to each other in the thumbnails), and so I don’t think I removed the 2nd part of the battery attachment as its in the 2nd photo. I figured it out later, but only after step 20, which requires that the battery is fully disconnected before doing. Oops!
Everything else went well though, and I’ve since reinstalled the battery, drained it, and recharged, and it seems to be fine. Will cross my fingers and hope I didn’t damage anything.