Gregory's Server@TechConnectify I don't remember the built-in tester on the battery itself, but I do remember the battery tester built into the packaging for Duracell batteries. I used it all the time.
These days, I use a dedicated battery tester to test my old batteries.
@Starcade @TechConnectify This was my first memory of these as well. I also remember noticing how they had integrated that into the batteries themselves.