For years I have linked my two (identical) batteries with a solid run of 4 ga. wire, with crimped-on terminals at both ends.  This effectively turns the two batteries into one LARGE battery.  What's critically important is to use VERY high quality wire and terminals.  If you have access to marine grade (West Marine on the Internet) I think that it's worth the price, as they assume that their equipment will be used in a very harsh electronic environment (salt air).

This is not a recommendation, but no problems have resulted.  However, I do have a good quality volt-meter that can be left on when the batteries are being used but the engine charging system is not (as when camped overnight).  I'm just cautious not to let the voltage drop below 11.8 in moderate weather.  

Fin Beven
'90 Carat, Custom Camper Conversion
Pasadena, CA
  ----- Original Message ----- 
  From: Joe Federici 
  To: vanagon@GERRY.VANAGON.COM 
  Sent: Monday, June 07, 2004 11:10 AM
  Subject: Re: Dual-Battery Question

  I wouldn't consider it safe but to each his own. That said if your
  going to do it I would use as large around 6 gauge or better and fuse
  it for sure it won't take much to over charge the battery and really
  BAD stuff can happen one you reach that point.

    The isolator or relay setup isn't that had to do maybe you could take
  it with you and hook it up on vacation?

  JFF

  On Jun 7, 2004, at 1:38 PM, Russell, William wrote:

  Well, after a weekend of work, I've managed to get my Optima Yellow top
  installed and the stereo switched over to it.  However, I have not yet
  installed a relay or isolator yet.  What I would like to do, for this
  trip
  (I leave tomorrow), is employ a manual system.  It would seem to me that
  hooking a wire from the + of the starter batter to the + of the Optima
  while
  the car is running would work.  I would like to use something a little
  more
  graceful than a jumper cable as I will be living in the van for the next
  week.  If I were to route a wire between the two batter compartments
  and use
  alligator clips to connect it, would this be safe?  What gauge of wire
  should I use?  Should it be fused?

  Any help is much appreciated.

  \/\/i!!y

  1980 Westfalia "Jazzy"