Chosen Solution
Got it sorted out. For anyone replacing their battery themselves on a MacBook Air - keep an eye on the ribbon cable that connects the keyboard and trackpad. It’s under the battery, and if you are not careful it can come out. Mine apparently came loose during the battery replacement and the connector end got lodged under the logic board, making it look like it was connected. I think mine must have been loose already because I didn’t notice it getting pulled on during the initial battery removal and re-install. There is a tiny tab on the top of the female side (on the logic board) that must be up in order for the ribbon cable connector (copper side down!) to go in. Once it’s in, you push the tab back down to secure the connector. Here is a vid that helped me. https://www.youtube.com/watch?v=BGPsUTWG… Whew. I’m not a tech, but feeling a lot better.
