USB Car Voltmeter - TOOGOO(R)Car USB Voltmeter Voltage Tester Digital Display DC 3-7,5V for Power Bank Simple and quick measurement of the voltage on the USB interface and the operating current of the device. Measurement accuracy: Voltage 10 mV, current 1 mA. Small and easy to carry, plug & play, no external power or other attachment required. To detect whether the output voltage/ output current from the USB charger reaches the standard or not.