Auxliary Battery
Click on thumbnails to enlarge photos
This is for a auxiliary battery to power the lights, sink pump, 
stereo, propane or gas heater etc. It's not used for starting 
the engine. If you use a dual battery for the appliances,
you will not drain the main battery.
In the unlikely event the main battery should fail, one
can use a short section of jumper cable and connect the
plus of the main battery to the plus of the auxiliary battery.

About auxiliary battery systems:
Some options:
1) A manual batt. switch can give you more flexibility.
You can switch between different batteries.
Drawback, one always has to switch back and
forth, to use the aux. batt., or to charge the aux batt.
The vanagon "Adventurewagen" has such a system.
2) A battery cut-out relay is very simple and relatively
inexpensive to install. 
It would be helpful to take a look at a Bentley diagram
of a weekender vanagon with an auxiliary batt. setup.
Some weekenders were factory-equipped with an auxiliary
battery system.
The GL full camper vanagons did not come with such a
system installed. In the diagram you can see the aux. batt.
and the main batt. It actually is a very simple diagram.
Click here to read more about relays.
3) It's also possible to use a battery isolator, but the
only one I know that's proven to work with the vanagon
is made by Sure Power Industries, and it's model 1202R.
It uses remote sensing to compensate for the voltage drop.
Most other battery isolators will not work with the Bosch alternator.
Click here to read more about isolators. I use the 1202R in
my '90 westy.

The auxiliary battery compartment in the westfalia camper
is not vented. It is possible to add two vents. Otherwise
one should use a sealed battery to prevent the build up of
fumes. A deep cycle battery will last longer
and give better service, but a regular vw battery will be
sufficient for limited use.
I used an Optima deep-cycle, and decided to install it upright.
The problem was that the battery posts stick out, because the
deep-cycle Optima is a few inches taller than a standard VW battery.
This is how I dealt with it. 
batterycover1.jpg (51497 bytes) Battery cover in place behind the driver's seat.
batterycover2.jpg (36562 bytes) Fiberglass cover for deep-cycle Optima battery. Driver's seat 
needs to be removed, 
and swivel-base rotated 180 deg. 
to gain access to the battery box

This is where the deep-cycle Optima battery lives.
I installed the Optima upright, and use a VW battery hold-down
bar. The 2 terminals are to the back.
I used hose clamps to fasten the connectors to the terminals.
There is not enough space for regular battery terminal-connectors.
(because of the swivel base of the seat)
batterycover3.jpg (38792 bytes) Here you can see the aux. battery
cut-off switch. I just used a 75 amp
pull-push switch. 

batterycover4.jpg (41008 bytes)

The small silver square cube is the original refrigerator 12 volt cut-off relay. The relay shuts down the refrig. when it's on the 12v setting and the engine is turned off, so the battery doesn't get drained.  Top center is a  45 amp thermal breaker for the charging wire. On the top left is a small fuse panel for the different appliances that run off the aux.battery.
batterycover5.jpg (32888 bytes) The underside of custom-made auxiliary battery cover, with the aux. batt. shut-off switch.
batterycover6.jpg (28472 bytes) Top of battery cover. You can see the 
raised back to make space for the 
battery posts. It is shaped so that the seat base can swivel freely.

Note: Disclaimer: You should double-check everything
with an automotive electrician..

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