First, I'm really supprised that among all of the list members, there is not
one single Electrical Engineer who steped foward to explain this relay
delema. So I'll give it to you in a nut shell: Guess what folks, if your aux
batt. is deeply discharged, and you're running 2ga. wire and a 75amp relay,
the batt. will most likely draw 75 amps(or whatever your alt. can put out) at
initial surge. But if you're running, lets say, a Hella relay, rated at
15amps, with the wiring provided, and with the same deeply discharged aux.
batt., you are most likely gonna draw about 12amps at initial surge, and much
lower after a short period of time. It's all related to the Gauge of the
Wire. Really. Don't buy it? Try this: Take that same deeply discharged batt.
and run a really, really tiny gauge wire directly from the positive post of
your cranker batt., to the positive post of the afore mentioned discharged
batt. Now start the engine. Did the wire smoke? Have the flames reached the
cockpit? Are you searching for that fire extinguisher(that is also probably
deeply discharged!)? NOPE. Your dead batt. will draw what the wire can
provide. Still don't belive me? Okay, lets see what VW did from the factory:
On older models equipted with dual batts, the relay was rated at 15amps( I'm
holding the original one out of my ' 79 Delux in my hand as we speak) and the
wire from said relay to the aux batt is 12ga. Believe me folks, nothing can
suck down a batt like the old style Dometic 12v/120v fridges found in the
pre-Vanagon Type 2's, and even when these batts are totally discharged,
starting your eng. does not cause a pyrotechnic display. If it did, VW would
have been litigated out of existance by now. If that still doesn't convince
you, well just flip through the pages of  Brightons Studies in Electron Flow
( My God, how I loathed that damn book when I was in college...) to get a
clearer picture. Your dead batt will only suck up as much as much juice as a
given wire will flow. 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.) Think of the set-up
as a "trickle charger". Okay, enough already.
Beckett