Karl Townsend wrote:

I often put a discharged dewalt or flashlight battery on the charger
and then forget to remove it. Am I hurting the battery? My better half
says I'm ruining them.

No way will I quit forgetting, should i get some sort of 120 volt
timer that only allows charging a couple hours a day?

Karl

It depends on the charger. Low $ tools are more likely to have simple
chargers that can damage batteries if left on the charger. High $ tools
particularly with chargers that are multi-voltage are more likely to be
smart and no damage batteries when left for long periods.