This 2-in-1 voltmeter plugs into your car's auxiliary power outlet to provide a readout of the car battery and a USB port for charging your small devices such as a phone or tablet. It is easy to install, has very low power consumption, and features a bright red LED display. What readout is normal for a car battery? After starting the car and engine is running (not driving), your car battery is healthy when the LED displays: Between 13.5 to 14.5 (12V Car) Between 26.0 to 28.0 (24V Car) When the engine off, and nothing turned on, your battery is healthy when the LED displays: Greater than 12.0 (12V Car) or 24.0 (24V Car) Specifications: Material: ABS Casing Color: Black LED Color: Red Output voltage: 5.0V Maximum output current: 2.1A