While driving down the road did you ever see a temporary roadside digital readout display sign of "This is your speed"? and then it gives the MPH you are driving.

My question is: Does a fuel cell power it? The plastic weatherproof enclosure seems to small to house a regular battery.

If it is a fuel cell would it need hydrogen cartridges? My very limited knowledge for a basic fuel cell power source is: oxygen + hydrogen = D.C. electric energy.

Frank

Most of those portable roadside displays are powered either by solar PV panels charging a battery, or (the larger ones) by a small diesel generator/battery setup. I haven't heard of a fuel cell being used for that application yet.

There are 2 types of fuel cells in common use, hydrogen/oxygen and methanol/air. the H2/O2 type would need a source of compressed gas, but the MeOH/air type runs on liquid fuel and oxygen from the ambient air.