12 Volt Direct Battery monitor is easy-to-use device that visibly and effectively displays how long the battery's charge or discharge will last. It also calculates how much power the battery has versus how much charge is going out, while providing the approximate amount of time the battery will remain charged. There is a wide range of battery monitors, depending on the specific application. Some of the more identifiable monitors include RV battery monitors, marine battery monitors and car battery monitoring systems.