The batt. is not an active device, like an electric
> motor, but a passive one, and will not suck your cranking batt dry at
> start-up (Unless you are running Massive gauge wire to the aux. batt. That
is > exactly why VW went with smaller relays and wire gauge.)

Beckett...

More likely VW was just saving a couple of bucks on the relays and wire
gauge.

If I understand your explanation of the battery not being an active device,
it seems to me that as a passive device a discharged auxiliary battery will
not be able to compete with the starter (active device). The starter will
get all or nearly all the juice from the starter battery. Once the engine
starts and the alternator turns the flow is reversed and the deeply
discharged auxiliary battery (and the starter battery) will then get the
charge.

I certainly have experienced no problem starting my van with a discharged
auxiliary battery connected to my starter battery with #4 wire. In fact, one
of the advantages of the larger wire is that if my starter battery is drawn
down I can flip a switch that by passes the relay and use the auxiliary
battery to assist the starter battery.

Bill