On Thu, 16 Dec 2010 23:39:20 GMT, (dan) wrote:

Karl Townsend wrote in
rec.crafts.metalworking on Thu, 16 Dec 2010 05:37:15 -0500:

I'm looking for a device and don't know what its called...

We've got two batteries on a diesel salt water boat. Looking for
something to charge the second battery only after the primary unit is
fully charged.

Right now, there is an isolator (which is just a couple large diodes)
that appears broken from years of sal****er corrosion. We're looking
to replace this. The idea here is to run the starter off one battery
and make sure its charged before going to the user battery.

Isolators suck, use a battery combiner.
http://www.hellroaring.com/index.php
Look like a pretty good system - more technical info would be nice
though.