HDE® Car Cigarette Lighter Battery Voltage Tester
This digital gauge displays the voltage of your car's battery. This gauge plugs directly into your cigarette lighter for an accurate reading on the current voltage.  When your engine is running the LED  should display: Between 13.5 TO 14.5  volts.  With the engine off, and nothing turned on, the LED should display: greater than 12.0 volts.