Battery testers are devices used to measure the voltage and power capacity of batteries. They can be used to determine whether a battery has enough power to operate a device, or to determine the remaining power level of a partially used battery. They are commonly used to test batteries in electronic devices such as cameras, flashlights, toys, and other battery-powered devices. Using battery testers can help users save money by identifying batteries that still have enough power and do not need to be replaced. Additionally, it can reduce waste by allowing for the proper disposal of batteries that are no longer usable.