Notebook computer vendors normally have DC power adapters for
use in cars to power notebooks. They take DC 13.8 volt input
and generate DC 19 volt (for HP notebooks) 3 - 4 amp output to
power notebooks. Such DC power adapters are quite expensive.
There are aftermarket DC inverters that are cheaper to get.

Using an inverter (13.8 volt DC in, 120 volt AC out) to power
a notebook AC adapter then power the notebook is indeed less
efficient. That's two stages of inverters.

If the setup is used only for charging the notebook you probably
will lose maybe 3 - 5 watts of power due to the inefficiency.
This will not be too much a concern really. But the reliability of
the inverter will be one to worry. Most cheap ones are over rated.
When they go bad they can cause damage to the device they power.

David

--- On Thu, 2/26/09, Loren Busch <starwagen@GMAIL.COM> wrote:

> From: Loren Busch <starwagen@GMAIL.COM>
> Subject: Re: Invertor ?
> To: vanagon@GERRY.VANAGON.COM
> Date: Thursday, February 26, 2009, 8:35 PM
> On Thu, Feb 26, 2009 at 8:03 PM, Edward Duntz
> <eduntz@hotmail.com> wrote:
>
> > You'd be better off using a dc power supply for
> the laptop.
>
>
> Ed has brought up a point I've tried to make in the
> past.   When selecting
> things that use power and will be used on the road try to
> go for those
> things that can be powered directly from the 12v aux
> battery.  I have only
> three items onboard that I have to use the inverter for,
> anything else can
> be powered or charged from a 12v outlet.
>
> >
> >
> >
> >
> >