12 or 24 volts for longer run time
As a general rule the higher the source voltage the more efficient the MOSFETs are at converting one voltage to another, or to AC. It has to do with current flow through wires and the MOSFETs and the transformer.

If you double the source voltage you could say you need just half the amps to get the same wattage output, but you also gain a few percent more efficiency in the conversion process.

That is one of the reasons many portable UPS systems use two 12 volt batteries in series, not in parallel. If they were in parallel the converter would have to work harder to overcome DC resistance to the higher current, which would be wasted away as heat.

There is talk of 36 and/or 48 volt car voltages, as the manufactures could use smaller gauge wire, so less copper and less cost in copper and weight. (For exposed wiring UL limits the voltage to 48 VDC or 36 VAC in the US, as this starts to create a mild shock if touched.)

Another example of why a higher source voltage makes for a more efficient converter; The Toyota Prius uses a 200 volt battery which it can boost to 500 volts to pass up a slow driver. A 200 volt source makes for a very efficient buck/boost converter.