On Thu, 16 Dec 2010 05:37:15 -0500, Karl Townsend
wrote:

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.

If his boat has a problem with that, perhaps an additional auxiliary
battery would be in order, and/or a heavier duty charging system.
(complete with welding option? AR AR AR!)

http://www.zena.net/htdocs/FAQ/toreplacealt2.shtml


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.

Google "charge isolator", which is used in RVs.
It won't separate charging times, but they work quite well.

--
Small opportunities are often the beginning of great enterprises.
-- Demosthenes