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.

HP
    HP Mini 311, 
    HP Mini 311-1012TU,
    HP Pavilion dm3,   
    HP Pavilion dm3-1000,
    HP Pavilion dm3-1023TX,
    HP Pavilion zx5180US,
    HP Pavilion zx5190US, 
    HP TouchSmart tx2-1375dx,

    HP Pavilion zv5000 Series 
        Pavilion zv5000, Pavilion zv5000t, Pavilion zv5000z,
        Pavilion ZV5100, Pavilion ZV5103, Pavilion zv5001US,
        Pavilion zv5001US, Pavilion zv5001US, Pavilion zv5002US,
        Pavilion zv5030CA, Pavilion zv5030CA, Pavilion zv5030US,
        Pavilion zv5030US, Pavilion zv5034US, Pavilion zv5034US,
        Pavilion zv5037WM
 
    HP Pavilion zv5100 Series
        Pavilion zv5101US, Pavilion zv5105US, Pavilion zv5120CA,
        Pavilion zv5120US, Pavilion zv5160CA, Pavilion zv5160US

   HP Pavilion zv5200 Series
        Pavilion zv5200, Pavilion zv5201, Pavilion zv5220US,
        Pavilion zv5255US, Pavilion zv5260US, Pavilion zv5270US

    HP Pavilion zv5300 Series
        Pavilion zv5300, Pavilion zv5310US, Pavilion zv5316US,
        Pavilion zv5320US, Pavilion zv5330US, Pavilion zv5340US,
        Pavilion zv5360US, Pavilion zv5370US, Pavilion zv5380US,
        Pavilion zv5390US

    HP Pavilion zv5400 Series
        Pavilion zv5400, Pavilion zv5404US, Pavilion zv5405US,
        Pavilion zv5410US, Pavilion zv5430US, Pavilion zv5460US

COMPAQ
    Compaq Presario A900

    Compaq Presario 1700 Series
        Presario 1700, Presario 1700AI, Presario 1700AP,
        Presario 1700AU, Presario 1700KR, Presario 1701AI,
        Presario 1701AP, Presario 1702AP, Presario 1702KR

    Compaq Presario 1710 Series
        Presario 1711AP, Presario 1712AP, Presario 1713AP,
        Presario 1714AP, Presario 1715AP

    Compaq Presario 1720 Series
        Presario 1721AP, Presario 1721LA, Presario 1721TC,
        Presario 1722AP, Presario 1722CA, Presario 1722EA,
        Presario 1722TC, Presario 1722US, Presario 1723SC,
        Presario 1723TC, Presario 1724SC, Presario 1724TC,
        Presario 1725A, Presario 1725EA, Presario 1725SC,
        Presario 1725TC

LG
    LG E500,
    LG LE50, T1,
    LG V1,
    LG Z1

    LG LS Series
        LS40, LS50, LS70, LS75

    LG LW Series
        LW20, LW25, LW60, LW65, LW70,
        LW75

    LG P Series
        P1, P300

    LG R Series
        R1, R200, R400, R405, R410,
        R500, R510, R700, R710