Purchased this item to display the Battery Voltage. The accuracy of the displayed voltage is very accurate (Nothing plugged into USB). The device is compact and well made. If you want to have an accurate battery voltage meter, this car charger get a 5/5. There is two minor issues with the device: The display is shiny, and it's difficult to see the voltage in sunlight due to reflections - especially at an angle & As the device is round, it's easy to plug it upside-don into the cigarette lighter. I will purchase this product again, as it's compact, well made and it gives an accurate battery voltage.