On Mon, 10 Aug 2009 08:51:15 -0400, "Lu Powell"
wrote:

I recently bought a used Champion brand bass boat. It has a battery
dedicated to the trolling motor that is not wired in to the charging circuit
for the cranking battery. The trolling motor battery gets charged at home
prior to a fishing trip.

Is there a simple fix that would let me charge both batteries at the same
time while on the water, and use the trolling motor battery without
draining the cranking battery?

The easiest solution is to use something called a "battery combiner".
It is essentially a voltage sensing relay that will connect both of
your batteries in parallel if the charging voltage exceeds a preset
level, and disconnect them when the charging voltage drops. The idea
is to allow charging both batteries when it's possible but prevent
accidently discharging your starting battery. It's a better
solution than a manual switch because it is all automatic with nothing
to remember.

Here are some examples:

http://www.defender.com/product.jsp?path=-1|328|51495|606044&id=605576

http://www.defender.com/product.jsp?path=-1|328|51495|606044&id=1212673