An auto DC adapter has a cigarette lighter input plug on one end that is plugged into the cigarette lighter receptacle and on the other a special output connector that is plugged into the laptop's power receptacle. Although recent P4 laptops have higher and higher power requirements, auto batteries have the capacity to supply the necessary output for the PC.

Dell
    Dell Inspiron i8000

    Dell Latitude C Series,
    Dell Latitude CP Series,
    Dell Latitude CS Series,
    Dell Latitude XPI Series,
    Dell Inspiron 2500 Series,
    Dell Inspiron 3700 Series,
    Dell Inspiron 3800 Series,
    Dell Inspiron 4000 Series,
    Dell Inspiron 5000 Series,
    Dell Inspiron 5000e Series,
    Dell Inspiron 5100 Series,
    Dell Inspiron 7500 Series,
    Dell Inspiron 8000 Series,
    Dell Inspiron 8100 Series,
    Dell Inspiron 8200 Series