It requires the SUN and there is no input for back power via usb or car charger. I installed it but due to lack of sunlight had to remove it. Plus my car is my garage most of the time so get very little to sun during the day to charge it. Sham really as the unit is well made even a bit on the expensive side.
Bought this motorhome and last owner left the screen display but removed the caps after following instructions they work really well and piece of mind also the gauge to check the tyre pressures is so simple not having to remove the cap and lose some pressure