1.Wide range of voltage meter:. DC4.5 ~ 40V Output current capability 2.5V/2A (note: the input voltage to a regulated output voltage of 5.0V when the 6.5 ~ 40V) 3. A button ("Output Enable" button) switch USB output a key ("low-power" button) to enter the ultra-low power 4. Car voltmeter can self-calibration will never exist without accurate voltmeter problem 5. With reverse polarity protection reverse polarity does not burn 6. With over-current over-temperature protection 7. With a USB power indicator 8. With terminal for easy access lines 9. High efficiency low ripple Instructions for use: After power-on module provides real-time detection voltage when you need to phone Ipad MP3 and other digital products charge touch "Output Enable" button to when USB power indicator lights USB 5.0V output voltage; when you need to turn off the digital control touch the "low-power" button then the module into ultra-low-power standby mode USB output accordingly shutdown. Module uses: Wide input voltage for car / battery car / motorcycle used for monitoring battery voltage battery status grasp can be used for a variety of voltage measurement purposes. 5.0V 2A of output current capability enough to meet a variety of USB devices voltage is very stable. Digital tube size: 22.6mm * 10mm (0.28 inch three integrated digital control)