Digital Voltmeter Monitor: Working voltage:12-28V Voltmeter measuring range:6V-30V Measuring DC voltage, with anti-reverse, short circuit protection Voltage indicator real-time monitor your vehicle's voltage, ensure the Equipment Safety Help monitor the storage-battery voltage, LED will alarm flash if the voltage is higher than 15V 11.3V-11.9V RED Led indicate the battery should be charged or replaced 12.0V-12.5V YELLOW Led indicate normal voltage when the car engine is OFF 12.6V-15V GREEN Led indicate normal voltage when the engine is ON