Timer for Battery-Powered Tools

Most hobbyists will have some tools that are battery-powered, such as a drill, screwdriver or power scissors. Unfortunately (and especially with cheaper devices) the batteries often seem to be empty when you need to use such a tool. This is usually caused by the self-discharge of the batteries. However, it’s not a good idea to continually keep the batteries on charge because the cheap chargers would ruin the batteries in the long term due to their constant charging current.