OK, it's Big Truck time.  OTR Truck Drivers have been using 12V appliances so long that they discovered inverters.  (Now change is not a word most drivers like.  "Eschew Change" is a common discussion topic in the "Drivers Only" part of most Truck Stop Restaurants.  In fact, since the Saudi's have bought most of the good Truck Stops, Drivers have been nonplused by the meatless buffets and porkless breakfasts.) 

So; the research & development cycles inside the cabs of Peterbuilts and Kenworths have been monumental.  The end result?

I own a specific inverter.  It is manufactured by "Cobra".  You remember, the CB-Radio people?  Well it turns out that they made so much money selling CB-Radios that they bought several small electronics companies.  One of those companies was Tripplite.  (Tripplite used to make the only decent "Fat Phoebes" in the world.  Right.  That's Nevada Test Site slang for a six or more outlet extension cord.  You've probably got one plugged into your PC right now.)

The Cobra power inverter model CPI 2500.  They make bigger ones (i.e. CPI 3500).  These particular inverters have four input connectors, two red (positive) and two black (Negative).  They are not to be used like you think they would be.

On a Big Truck, there is a string of batteries, usually four, or sometimes three, hooked in parallel.  They provide 12Volts at Oh my God what Wattage.  But if your truck is turned off, and you are off in Café Risqué for two or three days watching Sunshine and Jade and Amber dance... (Truckdriver fantasy, sorry about that image...  You can put it out of your mind...  Because you've never seen them dance!)  To begin again...  If you are home with the Wife and her Honey-do list and playing with the kids, when you get back to the truck, that inverter (in stand by mode) could have drained your batteries.  (It is cheaper to take a taxi to the nearest truck stop and buy four new batteries than to call one of those "mobil shop trucks" to come and jumpstart your truck.)

The procedure is that you hook one pair (black & red) to the first battery in the string of batteries; and hook the other pair of inputs to the last battery in the string.  The Inverter checks the load difference between the front battery and the back battery and if there is no current drain, it turns itself off.  (It leaves a tiny circuit running that could be powered for a year on a AA battery.)  That tiny circuit turns the whole thing back on when you turn on something that needs power...

I bought this last Cobra CPI 2500 from a retiring driver on eBay for about $200.00 a year or so ago.  You can find them in Truck Stops.

And... one more thing, for those of you so averse to change that you have a hard time getting up in the morning.  CostCo is selling 1000 Watt Xantex inverters for $26.95.  If you just have to try something and don't want to spend a lot to experiment...