Tried with a cleaned new battery. It beeps when I put the battery in, that is it. When I scan for unknown objects, I get shown an air tag, but it doesn't tell me anything about it. So probably I should just remove the battery - I must have gone through a heap of them debugging this - and just smash it.

Oh yeah totally, that “feature” of a Duracell cr2032 battery screwed me over in that exact case. They just don’t work at all with an AirTag (battery bought from afaik reputable supplier, Home Depot). Switched to Energizer cr2032 and it’s been great.

Thats worth a try, because if the batteries have that, trying several ones of the same brand would produce the same results.

Now, do I try to test this by licking the battery or should I try to sand the surface without pre-testing? :)