Reddit reviews Zeltauto LED Digital Car Voltmeter 12V/24V Vehicle Voltage Gauge Monitor for Auto Car Truck (1)

With red screen digital color, there is no difficulty in seeing the display; Apply for DC 12V or 24V car; Measuring range: DC 8V-30V+/-1.2% (The voltage of car usually reads 12V±0.5V when it works; PLEASE ALLOW 0.1-0.5 VOLTS DISPLAY ERROR)This digital gauge displays the voltage of batteries in the car; Powered by car cigarette lighter chargerSimple enough to use, just plug it into cigar lighter socket, watch alternator's output from idle to accelerated speedWhen engine running (do not drive), the LED display: between 13.5 to 14.5 (12V car), between 26.0 to 28.0 (24V car)When engine off, and nothing turned on, LED display: Greater than 12.0 (12V car) or 24.0 (24V car)