Swerving back to the original subject, I’ve got too many single-cell chargers in my Do Not Use bin because if left charging for a while they fail to cut off at 4.2v.
“DeWorld” brand from a Radio Shack sale is one of them. The other is just labeled “Charger” — both made in China of course.

A voltmeter or multimeter is cheap insurance to have when messing with these things.