You need electricty to power a fan that puts oxygen into the combustion chamber & for the ignition spark, but the amount of power needed is very small you can actually use a converter and run it off the van battery
they arn't portable and are used with truckmounted units or for portables that stay in the van.
they are unbeatable for producing hot water, even the biggest truckmount cannot match the temp at such high flow rate they produce (140' at 21L/M)
Mike