A battery-operated power output device includes a battery seat for receiving a dry cell power source, a charging signal generator connected to the battery seat for generating a charging signal output, a power source connector for connection to a rechargeable battery load, a safety switch for making or breaking connection between the power source connector and the charging signal generator, a detecting module for detecting voltage and current values of the charging signal output, and a switch controller that controls the safety switch according to a timer signal from a timer unit and detected voltage and current values from the detecting module.