For an aux battery to be beneficial all loads to be used when not driving have to be wired to it and it has to be isolated from the chassis battery when not being charged. From the factory, the alternator has to actually be charging for the fridge to work.

Dennis 

Sent from my Windows Phone

-----Original Message-----
From: Loren Busch
Sent: Friday, June 10, 2011 3:07 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Really Dumb Question About Aux Batteries Install.

> Both of the Westfalias I've owned came with an aux battery installed under
> the drivers seat.  Never paid much attention in the first one, my '85.  But
> in my '90 I found out the hard way that the aux was essentially hard wired
> to the 'fridge, would run the aux dry in about two hours.  I now have a much
> more complicated setup in my '90 that I understnad, not at all stock.
> But I've just been thinking about the from-the-factory Westy wiring (no aux
> battery in place) where the 'fridge can only be run on 12v with the ignition
> on, engine running.  And then trying to remember what the configuration is
> IF and aux battery is installed, with a relay added, according to the
> Bentley wiring diagrams.  My understanding is that the 'fridge is, with that
> install, still only going to work with the engine running.  And I know that
> all the accessories will still be on the starting battery.  So, what is
> gained by installing an aux battery (according to Bentley)?  What am I
> missing, I obviously don't understand (or misunderstand) something.