It seems to be consensus that the correct way to hook up an aux 
battery in our vans is to use a 'combiner' relay and not use an RV 
'isolator'.  Fine.

But a problem remains when the aux battery is heavily discharged and 
the vehicle is started.  The discharged battery can draw a very heavy 
current load until battery voltage comes up.  Something in the order 
of 30, 60, or even 100 amps.  This also has a disadvantage of 
prodcuing gobs of H2 gas (acutally H2 and O2 in a exquisitely 
explosive combination) if a conventional deep cycle battery is used.  
Very heavy battery cables are the order of the day, in addition to a 
sealed battery box.

Isn't there an electronic device that could limit the charging 
current in the conductor going to the aux battery?   I can't picture 
what it would be in my mind but there must be something out there.

It would need to:
- not interfere with the terminal charging voltage

- be self-adjusting to limit current to say, 30 amps but also let a 
trickle of 1 or 2 amps thru to top off the battery when it isn't 
fully discharged.

- be electrically efficient and not create a dangerous amount of 
heat.

I think this would solve the problem of melted aux wires when just 10 
ga. is used and also alleviate having to run large battery cables all 
over the place.

Oh.  and i'd also like a device i can attach to my fuel line that 
would double my gas mileage.

-dan

Daniel Houg
Section of Drinking Water Protection
Minnesota Department of Health
voice: 218/755-3820