For what it is worth I have been using a Sure Power separator on Franks
recommendation for a few months now.  It is working great and installs
really easy.
Billy
http://www.surepower.com/separator.html

On 7/19/07, Dennis Haynes <d23haynes57@hotmail.com> wrote:
>
> The sure power isolator or smart relay is actually a voltage controlled
> relay. It connects the two battery banks when either one is being charged.
> When the charge source stops and the voltage returns to a battery only
> state, the banks are again isolated.
>
> Dennis
>
>
>
> >From: Kenneth Lewis <kdlewis@NORTHSTATE.NET>
> >Reply-To: Kenneth Lewis <kdlewis@NORTHSTATE.NET>
> >To: vanagon@GERRY.VANAGON.COM
> >Subject: Re: Aux Battery Charging Alternatives Question for the
> Electrical
> >             Gurus
> >Date: Wed, 18 Jul 2007 18:57:57 -0400
> >
> >Loren,
> >    Personally, I would add a relay that connects the aux battery (to the
> >alternator)only  when the car is running. Otherwise you run the danger of
> >discharging both batteries.
> >    I would not use steering diodes due to the loss of precious
> electrons.
> >    When in camping mode, I am too lazy/forgetful to use a marine battery
> >selector.
> >Ken Lewis
> >http://neksiwel.20m.com/
>