...except when the slot is too narrow for it to fit, or so wide it slips and buggers the edges.
Most of the older cameras I've been messing with have a little circular battery cover on the bottom, to accommodate a range of batteries from the '60s era mercury cells (or their modern zinc-air substitutes) on the old Leicaflex SL to the familiar lithium CR123 that drops into the mid-'90s Contax TVS. These typically have the dished slot to allow the use of a coin as a screwdriver, but there doesn't seem to be any standardized thickness of coin preferred amongst the different makers.
Fortunately, Bobbi gave me a handy little gizmo to settle that problem: A coin screwdriver with a varying-thickness rim. It's handy. I should get more.