The Calterm vehicle battery tester is designed for monitoring the voltage of 12V or 24V batteries by simply inserting the tester it into a cigarette lighter socket. Once plugged in the Calterm vehicle battery tester will instantly display the exact voltage of the battery and a easy to understand LED indication if the battery is good / weak or in need of immediate replacement. The display and charging system will show the voltage of the battery, meanwhile the instrument will also give LED indication and bar indication, so you can determine the charge level of the battery. The Calterm vehicle battery tester provides a peace of mind and is an essential tool for every vehicle.