Inverter limitation on our Prius?

That's right. You won't be able to use that inverter to its full potential unless you wire it straight to the battery yourself. Some inverters even come with spring clips to let you do just that. You can plug it in and use it with very low powered things just the way it is, but there isn't any protection to keep you from blowing the fuse feeding that cig socket.

Alternately you can wire up your own quick-disconnect connector somewhere near the battery so you can add/remove the inverter easily whenever you want. Please include a fuse on the + leg as close to the battery as possible for fire safety.

 

Right, you should find the 120 watt limit on the cig outlets in the car printed right on them.

When going directly to the battery, if you're planning to use 500 watts, remember that'll be over 40 amps from the 12 volt system. There might be little springy clips with your inverter to clip on at the battery, but they may be flaky or get warm at that kind of current. A properly sized, fused wire that you directly bolt on will be better.

Look closely at the car's + battery post connector, that plastic shape that sort of drapes over the side of the battery like a Dalí watch. That's a fusible link, and the bolt at its lower end, where the car's power cable attaches to it, is a good place to tap off your connection. Then that fusible link is between your connection and the battery, and the car's underhood DC/DC fuse is between your connection and the converter.

 

so.. funny.. i just wrote an article about this, well in a way... my thoughts on choosing a proper inverter .. just get the kind where you can swap between cig plug and battery clamps.

these days I run two 2,000W pure sine inverters, each with its own 85ah battery.