DROK Green LED Digital Gauges Automotive Monitor 12 V Car Colck Panel Voltmeter Thermometer 3in1 Power Supply: DC 7-30V ( with anti-reverse protection ) Display: Four 0.56 " Green LED digital tube Measuring temperature: -55 to 125c Measuring voltage: Range 0-33VDC Clock: 24-hour,power off memory function, the battery backup is available 3-4 years