I bought an AA battery case, bored a small hole in the caliper's battery cover, fed wires through, secured them to the contacts and used velcro to hold the AA battery case to the back of the caliper. I can easily take the battery out when storing and it always just works without having to buy overpriced button cells. It does look a bit janky.
Might be a 2xAA case. They’re the most popular, anyway (because 1.5v electronics are relatively new so it was either 3.3v running off the two batteries or boosted to 5v and you can’t really boost 1.5v to 5v cheaply, effectively, or for long).
