Reentrant formulated the question :
Our water meter has a wireless module ("Everblu Cyble"). Their data sheet
says "battery - lithium, 15 years / 10 years in fixed network mode"

I have no idea how my water meter works at all, but they seem to be
able to interrogate it from the road, some way from the back of the
house where the meter is. The meter is a mechanical one in what looks
like a brass body.