Car adapters are DC / DC聽 regulated converters, which work with a variety of mobile devices such as radios, television sets, CD players, computer equipment and GPS. They are used in places where mains power is not available (eg. in the car, outdoors, on boats and yachts).
You just need to plug a car adapter into the cigarette lighter socket and you can immediately use the equipment, usually powered with batteries or rechargeable batteries.