Ok so if you want to run it from your car you could mount it somewhere in the back, then connect your vehicle's aux. battery ( if you have one ) via thickish cables, into where the internal batteries would normally go. I am assuming the orginal batteries were 12V ( or input to the inverter at least was 12V ) ?
you'd need fairly thick cables between the battery and the UPS
Pity it doesn;t appear to have standard 3 pin socket outlets - looks like anything 240V AC you want to run from the UPS/Inverter ,you'd need to put a special plug on it, or make an adaptor.

