Jay,
Here's how the dual battery system in my Westfalia looks like:
Main battery is behind the pass seat. No. 2 AUX is under the rear seat.
A 4-way boat battery switch manages them like this:
Both supply power thru the main fuse block. No need to run extra wire.
When you want to run off #2, switch to #2, and likewise for #1. And you can
switch to #ALL, which is where you leave it to charge both batteries (this is
best for when both batteries are same size and condition.
Since different size and condition batteries charge at different rates, the
alternator regulator will taper off the charge sensing the more fully charged
battery, leaving the second battery undercharged. In this case you switch to
1# half the time and #2 the other half, so that one battery gets the full
alternator output.Wireing up the switch is simple. The pass # 1 batt cable is
disconnected from the starter and connected to the #1 terminal of the switch.
New cable is connected to the starter and goes to #COMMON on the switch.
A shorter cable is attached to #2 on the switch. Second battery is grounded
at a seat belt mounting point.
In my set up, the switch sits on top of the rear seat heater box.
Having a switch within reach while driving is not a good idea, since
switching while the engine is running will ruin the alternator.
Isolators waste a volt, and have trouble sensing 2 batteries at a time.
The other advantage of this set up is the cables used are battery size, a
turn of the switch and the good battery will start your motor-you will almost
never need a jump start again.
A good switch is the Guest 4-way for $23.99 at West Marine
(www.westmarine.com)
Happy New Year!

Robert

Robert Keezer

1982 Westfalia
1983.5 Sunroof Vanagon
1980 Westfalia

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