Aonengdun Convenient 3-in-1 Car Charger to Car Cigarette Lighter + 2 USB w/ Voltage Monitor - Black
For 12V cars the voltage monitor shows battery voltage before starting (11.9~12.8V normal) and shows motor voltage after starting it (13.4~14.8V normal); For 24V cars the voltage monitor shows battery voltage before starting (23.9~25V normal) and shows motor voltage after starting it (25.5~27V normal).