The BATMAN Battery Monitor is a unique device that measures the charge that has been used from your 12-volt batteries. At a touch of a button, the used capacity displayed is in Ampere-Hour (U). The Ampere-Hour indicates the amount of total energy that a battery was able to deliver at its rated voltage. Therefore, being able to see the AH used becomes a critical indication when you rely on batteries for all your energy requirements when camping or even in your home. In short, every time you have a big battery, you need a BATMAN monitoring system to show you the state of your battery.