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 COMPAQ
    HP Compaq 4320t Mobile Thin Client,
    HP Compaq 6535s,
    HP Compaq 6720t Mobile Thin Client,
    HP Compaq Business Notebook tc4400,
    HP Compaq Mini-Note 2133,
    HP Compaq tc4200 Tablet PC,
    HP Compaq tc4400 Tablet PC
  
    HP Compaq Presario B1200 Series
        Presario B1210 

    HP Compaq Business Notebook Series
        Business Notebook 2210b, Business Notebook 2510p,
        Business Notebook 2710p, Business Notebook 8510p,
        Business Notebook 8710p

    HP Compaq Business Notebook 6000 Series 
        Business Notebook 6510b, Business Notebook 6515b,
        Business Notebook 6520s, Business Notebook 6531s,
        Business Notebook 6710b, Business Notebook 6710s,
        Business Notebook 6715b, Business Notebook 6715s,
        Business Notebook 6720S, Business Notebook 6820S,
        Business Notebook 6910p  
 
    HP Compaq Business NoteBook nc Series
        Business NoteBook nc2400, Business Notebook nc2410,
        Business Notebook nc4200, Business Notebook nc4400, 
        Business Notebook nc6140, Business Notebook nc6220,
        Business Notebook nc6230, Business Notebook nc6320,
        Business Notebook nc6400, Business Notebook nc8430

    HP Compaq Business NoteBook nx Series
        Business Notebook nx6115, Business Notebook nx6125,
        Business Notebook nx6130, Business Notebook nx6310,
        Business Notebook nx6315, Business Notebook nx6320,
        Business Notebook nx6325, Business Notebook nx6330,
        Business Notebook nx7300, Business Notebook nx7400,
        Business Notebook nx8410, Business Notebook nx9420,
        Business Notebook nx9600

    HP Compaq Pavilion dv3000 Series
        Pavilion dv3022TX

    HP Compaq Mobile Workstation Series
        Mobile Workstation nw8240, Mobile Workstation 8510w,
        Mobile Workstation nw8440, Mobile Workstation 8710w,
        Mobile Workstation nw9440, Mobile Workstation nx8420

COMPAQ
    Compaq 2230s,
    Compaq 2510p,
    Compaq 2710p,
    Compaq 320,
    Compaq 321,
    Compaq 420,
    Compaq 421,
    Compaq 430,
    Compaq 435,
    Compaq 511,
    Compaq 550,
    Compaq 610,
    Compaq Compaq 615,
    Compaq 650,
    Compaq 6510b,
    Compaq 6530b,
    Compaq 655,
    Compaq 6710b,
    Compaq 6720t Mobile Thin Client,
    Compaq 6830s,
    Compaq 8710p,
    Compaq EliteBook 2170p,
    Compaq EliteBook 2570p,
    Compaq EliteBook 8470p,
    Compaq EliteBook 8530p 2133 Mini-Note PC,
    Compaq EliteBook 8560p,
    Compaq EliteBook 8570p,
    Compaq Folio 13,
    Compaq Mini 311c-1100,
    Compaq Presario C700,
    Compaq Presario CQ32,
    Compaq Presario CQ36-100,
    Compaq Presario CQ41-100,
    Compaq Presario CQ42,
    Compaq Presario CQ50-200,
    Compaq Presario CQ57-200,
    Compaq Presario CQ72,
    Compaq Presario F700,
    Compaq Presario V3700,
    Compaq Presario V3800,
    Compaq Presario V3900,
    Compaq Presario V6600,
    Compaq ProBook 430 G1,
    Compaq ProBook 4340s,
    Compaq ProBook 4540s,
    Compaq ProBook 4545s,
    Compaq ProBook 4740s,
    Compaq ProBook 6475b,
    Compaq ProBook 6570b,
    Compaq Spectre XT Pro Ultrabook

    Compaq 6730 Series
         6730b, 6730s

    Compaq 6735 Series
        6735b, 6735s

    Compaq 8510 Series
        8510p, 8510w Mobile Workstation

    Compaq Presario CQ20 Series
        Presario CQ20-100, Presario CQ20-200, Presario CQ20-300

    Compaq Presario CQ35 Series
        Presario CQ35-100, Presario CQ35-200, Presario CQ35-300

    Compaq Presario CQ40 Series
        Presario CQ40-100, Presario CQ40-300, Presario CQ40-400,
        Presario CQ40-418AX, Presario CQ40-500, Presario CQ40-600,
        Presario CQ40-700, Presario CQ41-200, Presario CQ42-100,
        Presario CQ42-200, Presario CQ42-300, Presario CQ43-100,
        Presario CQ43-300, Presario CQ43-400, Presario CQ45,
        Presario CQ45-100, Presario CQ45-300  

    Compaq Presario CQ56 Series
        Presario CQ56-100, Presario CQ56-200

    Compaq Presario CQ60 Series
        Presario CQ60-100, Presario CQ60-200, Presario CQ60-300,
        Presario CQ60-400

    Compaq Presario CQ61 Series
        Presario CQ61-100, Presario CQ61-200, Presario CQ61-300,
        Presario CQ61-400

    Compaq Presario CQ62 Series
        Presario CQ62-108TX, Presario CQ62-200, Presario CQ62-300,
        Presario CQ62-400, Presario CQ62-a00

    Compaq Presario CQ70 Series
        Presario CQ70-100, Presario CQ70-150EG, Presario CQ70-200

    Compaq Presario CQ71 Series
        Presario CQ71-100, Presario CQ71-200, Presario CQ71-300,
        Presario CQ71-400

HP
    HP 230W Docking Station,
    HP 500,
    HP 540,
    HP 620,
    HP 625,
    HP 630,
    HP 635,
    HP 8510w Mobile Workstation,
    HP 8710w Mobile Workstation,
    HP 90W Docking Station,
    HP Pavilion 14-c010us,
    HP Pavilion g4-1300,
    HP Pavilion g3200 Desktop,
    HP Revolve 810

    HP EliteBook Series
        EliteBook 2540p, EliteBook 2560p, EliteBook 2740p,
        EliteBook 2740p Tablet PC, EliteBook 2760p, EliteBook 6930p,
        EliteBook 8440p, EliteBook 8440w Mobile Workstation, EliteBook 8460p,
        EliteBook 8460w, EliteBook 8530p, EliteBook 8530w,
        EliteBook 8530w Mobile Workstation, EliteBook 8540p, EliteBook 8540w Mobile Workstation
        EliteBook 8560p,
        EliteBook 8560w Mobile Workstation, EliteBook 8730w, EliteBook 8730w Mobile Workstation,
        EliteBook 8740w Mobile Workstation, EliteBook 8760w Mobile Workstation,
        EliteBook Folio 9470m Ultrabook

    HP Envy Series
        ENVY 14-2000, ENVY 15-3000, ENVY 17-2000,
        ENVY 6t, ENVY Ultrabook 4t-1100, Envy 14 Spectre,
        Envy 14-1000, Envy 14-1100, Envy 14-1100 Beats Edition,
        Envy 14-1108TX (Beats), Envy 14-1108TX Beats Edition, Envy 14-2000,
        Envy 15, Envy 15-1000, Envy 15-1009TX,
        Envy 15t-3200, Envy 17-1000, Envy 17-1100,
        Envy 17-2000, Envy 17t-3200, Envy 17t-3200 3D Edition,
        Envy 4, Envy 6-1002tu, Envy 6-1007tx,
        Envy SleekBook 4-1055tu, Envy SleekBook 6-1101tx

    HP Folio Series
        Folio 13-1000, Folio 9470m-08012000000, Folio 9470m-08012000010,
        Folio 9470m-08012000030, Folio 9470m-08012000080, Folio 9470m-08019000000,
        Folio 9470m-08019000010, Folio 9470m-08019000030, Folio 9470m-08019000080,
        Folio 9470m-0801b000000, Folio 9470m-0801b000010, Folio 9470m-0801b000030,
        Folio 9470m-0801b000080, Folio 9470m-11012000000, Folio 9470m-11012000010,
        Folio 9470m-11012000030, Folio 9470m-11012000080, Folio 9470m-11019000000,
        Folio 9470m-11019000010, Folio 9470m-11019000030, Folio 9470m-11019000080,
        Folio 9470m-1101b000000, Folio 9470m-1101b000010, Folio 9470m-1101b000030,
        Folio 9470m-1101b000080, Folio 9470m-21012000000, Folio 9470m-21012000010,
        Folio 9470m-21012000030, Folio 9470m-21012000080, Folio 9470m-21019000000,
        Folio 9470m-21019000010, Folio 9470m-21019000030, Folio 9470m-21019000080,
        Folio 9470m-2101b000000, Folio 9470m-2101b000010, Folio 9470m-2101b000030,
        Folio 9470m-2101b000080, Folio dm3

    HP G Series
        G32, G42, G56-100, G6000, G60-100, G60-120US,
        G60-200, G60-400, G60-500, G61-300, G61-400,
        G62-100, G62-200, G62-a00, G62-b00, G7000,
        G70-100, G70-200, G70-400, G71-300, G72-100,
        G72-200, G72-a00, G72-b00

    HP HDX Series
        HDX X16-1000, HDX X16-1100, HDX X16-1200,
        HDX X16-1300, HDX X18-1000, HDX X18-1100,
        HDX X18-1200, HDX X18-1300

    HP Mini Series
        Mini 311-1000, Mini 311c-1000,
        Mini 5102, Mini 5103

    HP Pavilion dm1 Series
        Pavilion dm1, Pavilion dm1-1000, Pavilion dm1-1100,
        Pavilion dm1-2000, Pavilion dm1-2100, Pavilion dm1-3000AU,
        Pavilion dm1-3100, Pavilion dm1-3200, Pavilion dm1-4100,
        Pavilion dm1-4100AU, Pavilion dm1-4200, Pavilion dm1-4200sa,
        Pavilion dm1-4200sb, Pavilion dm1-4200sg, Pavilion dm1-4200sh,
        Pavilion dm1-4200sp, Pavilion dm1-4201au, Pavilion dm1-4201er,
        Pavilion dm1-4201sr, Pavilion dm1-4202au, Pavilion dm1-4203au,
        Pavilion dm1-4205au, Pavilion dm1-4206au, Pavilion dm1-4208au,
        Pavilion dm1-4209au, Pavilion dm1-4210au, Pavilion dm1-4210ej,
        Pavilion dm1-4210sc, Pavilion dm1-4210sd, Pavilion dm1-4210sw,
        Pavilion dm1-4210sx, Pavilion dm1-4210us, Pavilion dm1-4211au,
        Pavilion dm1-4212au, Pavilion dm1-4213au, Pavilion dm1-4214au,
        Pavilion dm1-4216au, Pavilion dm1-4220ez, Pavilion dm1-4222ej,
        Pavilion dm1-4225sw, Pavilion dm1-4230sf, Pavilion dm1-4230sp,
        Pavilion dm1-4230sw, Pavilion dm1-4231sf, Pavilion dm1-4232sf,
        Pavilion dm1-4233sf, Pavilion dm1-4240sf, Pavilion dm1-4240so,
        Pavilion dm1-4250ew, Pavilion dm1-4269ca, Pavilion dm1-4270la,
        Pavilion dm1-4290ss, Pavilion dm1z-4200 CTO

    HP Pavilion dm3 Series
         Pavilion dm3, Pavilion dm3-1000, Pavilion dm3-1100,
        Pavilion dm3-2100, Pavilion dm3-3010us

    HP Pavilion dm4 Series
        Pavilion dm4-1000, Pavilion dm4-1100,
        Pavilion dm4-1300, Pavilion dm4-3000

    HP Pavilion dv Series
        Pavilion dv2-1000, Pavilion dv2-1100, Pavilion dv2600,
        Pavilion dv2700, Pavilion dv2800 Artist, Pavilion dv2800 Verve,
        Pavilion dv2900, Pavilion dv3-1000, Pavilion dv3-1100,
        Pavilion dv3-2000, Pavilion dv3-2100, Pavilion dv3-2137TX,
        Pavilion dv3-2200, Pavilion dv3-2232TX, Pavilion dv3-2300,
        Pavilion dv3-4000, Pavilion dv3-4100, Pavilion dv3-4200,
        Pavilion dv3-4300, Pavilion dv3100, Pavilion dv3500,
        Pavilion dv3600, Pavilion dv3700, Pavilion dv4-1100,
        Pavilion dv4-1200, Pavilion dv4-1300, Pavilion dv4-1400,
        Pavilion dv4-1500, Pavilion dv4-2000, Pavilion dv4-2100,
        Pavilion dv5-1100, Pavilion dv5-1200, Pavilion dv5-1300,
        Pavilion dv5-2000, Pavilion dv6-1000, Pavilion dv6-1100,
        Pavilion dv6-1200, Pavilion dv6-1300, Pavilion dv6-1400,
        Pavilion dv6-2000, Pavilion dv6-2100, Pavilion dv6-3000,
        Pavilion dv6-3200, Pavilion dv6-3300, Pavilion dv6-4000,
        Pavilion dv6-6c00, Pavilion dv6t, Pavilion dv7-1100,
        Pavilion dv7-1200, Pavilion dv7-1400, Pavilion dv7-2000,
        Pavilion dv7-2100, Pavilion dv7-2200, Pavilion dv7-3000,
        Pavilion dv7-3100, Pavilion dv7-4000, Pavilion dv7-4100,
        Pavilion dv7-4300, Pavilion dv7-5000, Pavilion dv7-6c00,
        Pavilion dv8, Pavilion dv8-1000, Pavilion dv8-1200,
        Pavilion dv9600

    HP Pavilion g6 Series
        Pavilion g6-1300, Pavilion g6-1365ea

    HP Pavilion tx Series 
        Pavilion tx1100, Pavilion tx1400, Pavilion tx2000,
        Pavilion tx2100, Pavilion tx2500, Pavilion tx2600

    HP ProBook Series 
        ProBook 4230s, ProBook 4320s, ProBook 4321S,
        ProBook 4330s, ProBook 4420s, ProBook 4425s,
        ProBook 4430s, ProBook 4520s, ProBook 4525s,
        ProBook 4530s, ProBook 4535s, ProBook 470 GO,
        ProBook 4720s, ProBook 4730s, ProBook 5310m,
        ProBook 5320m, ProBook 5330m, ProBook 6360b,
        ProBook 6440b, ProBook 6450b, ProBook 6455b,
        ProBook 6460b, ProBook 6465b, ProBook 6540b,
        ProBook 6545b, ProBook 6550b, ProBook 6555b,
        ProBook 6560b

    HP TouchSmart Series 
        TouchSmart tm2-1000, TouchSmart tm2-1001TX, TouchSmart tm2-2000,
        TouchSmart tm2-2100, TouchSmart tx2-1000, TouchSmart tx2-1100,
        TouchSmart tx2-1200, TouchSmart tx2-1300