Reply #11: I manage with just a 400Watt inverter (320 watt continuous)

[ConcernedCanuk]

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Mind you, the sump pump only consumes 3 amps(120V x 3 = 360 watts)

So the amperage and wattage of the sump pump would be the factor here.

If one put wires to the outside to be able to connect to their vehicle;

one wouldn't even need to buy an extra battery.

Caution:

I've found some converters do not operate properly if the vehicle is running - so use the inverter when your vehicle is NOT running.

SO

a little wiring, a $100 inverter

problem solved