For whatever it is worth I have a small version of what you describe.
It's a small case with a couple of 6V motorcycle batterys with outlets for
12, 9, 6, and 3 volts. It also has 2 large lugs on the back that are to be
used as a starting "assist". I never tried the "assist". I imagine its not
worth much, but then again one may not need that much in some situations.
   Picked it up at a yard sale for $5 with the intention of using it to
power a small B&W TV. Works fine for this. Watching for a few hours at a
time did not run it down and it recharged from the lighter in a couple of
hours.
   If mine can power a TV for a couple of hours I suppose yours can power a
cell phone on standby all night.

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com]On Behalf
Of Jim Fritz
Sent: Sun, April 04, 1999 10:23 PM
To: vanagon@GERRY.VANAGON.COM
Subject: 2nd battery...an alternative??

Volks,
I've listened to all of the various ways many of you have devised to make a
2nd battery work in your Westys.  You folks are very ingenious!  However,
after reading the excellent post by Bill Davidson about what he did to hook
up his battery in his Synchro, I knew I was in WAY over my head.  So, being
basically lazy, I went looking for an easier solution that might answer all
of these same issues with out the headaches.  I'd like your comments, roses
or thorns, regarding what I am considering doing.
Basically I've found one of these sealed 600 amp lead batteries that come
with jumper cables attached, a 12v DC power port, 110-v power outlet,
worklight, AC charging cord, DC power inverter/charging cord, built-in cord
storage,  and battery level indicator.  Its supposed to hold an 8-12 hour
charge orver 6 months.  The ad says it will power a standard house lamp for
8 hours so who knows how long you could run a cell phone or laptop?!  You
can store it on its side or upside down because its sealed and charge it
from your cigarette lighter as you go down the road.  It costs $160 so its
not cheap but it eliminates the electrical engineering degree (which cost my
brother big $$ and 4 years at Iowa State) and I can transfer it to other
vehicles and other outdoor adventures.  It looks like its about 16" X 16" X
4" and a similar one that I saw weighed about 20-30 lbs.  What's your
thoughts on this easy way out?
Jim in Iowa
91 Passat Wagon GL
89 Westy
66 Beetle