There may be other more technical reasons to NOT connect both
batteries directly, but the simplest one is separating them means you
usually have one good battery to start you vehicle with if you leave
your headlights / fridge, etc. on anf forget.

There is a decent article on wiring two seperate batteries at:
http://www.vanagon.com/info/articles/upgrades/battery/index.html

Chris

On 8/15/06, Shawn Luft <shawnagan@sympatico.ca> wrote:
> Hi,
>
>
>
> I just installed a heavy duty deep cycle battery under the rear bench.
>
> Is it ok to leave this battery connected to the main battery lead all the
> time?  Or will the 2 batteries somehow drain each other?
>
>
>
> Thanks :-)
>
> Shawn
>