I do parking lot onroad with my brother and his son. we use either 1 or 2 large SLA batteries with a 100 watt solar panel and its good to go all day for the 3 of us running a total of 5 cars. charger pulls up to 15 amps on 2, 2s packs and batteries are fully charged when we leave. no reason to use power supply when charger runs on DC.

this is basically the same size battery that we run. its maybe 1/3 the volume of a car battery. not terrible to carry.