Thanks so much for the thoughts! The idea of using solder paste is intriguing, since it would take less heat to get it to actually melt, though I feel some concern about my own ability to line up the pads and the holes without smearing the solder paste in places that it doesn’t belong.
I had another idea for this, inspired by the castellated vias on the side of the ESP32 breakout board. I’d make one larger unplated oval hole that exposes the pads, then add a couple plated half-holes on the top and bottom that would sit on top of the battery pads. That should give me more room to maneuver the soldering iron without needing to line things up quite so carefully. It would look something like this:
The light yellow ovals represent where the BAT pads are; the bigger orange oval is the unplated opening; and the fat yellow half-circles are the places where I’d actually make the connection.
Any thoughts on whether this is a good or bad idea? Would this violate any common design principles? KiCad won’t let me actually set a 0.00mm diameter for the plating of the big oval, and when I set it to 0.1mm it says “Warning: pad hole will leave no copper”, but that’s what I actually want.