Batteries use to have a power check mechanism.

There was a small white circle on the copper top side and a half circle on the bottom non nipple side.

What you needed to do was cover the white circle on side of battery with a thumb and then cover the whole bottom with other thumb and the indicator would tell you how much the battery had left.

Since it was a half circle off the bottom many people didn’t know they were supposed to cover up the whole bottom. Making it hard for many to use it because you’d have to press down very hard on the edge to get it to work.