On Mon, 07 Sep 2009 12:40:00 -0400, JohnH
wrote:

Yesterday I left the accessory switch with the radio and gps on while
we were at the beach, about four hours. I've put a battery cut off
switch in the boat, and that has prevented the 'accidental' rundown of
the battery while sitting in the marina. The boat started fine when we
left, but after sitting at the beach for four hours it would do only
the rrrr.....rrrr......rrrr....bit. One of the guys who'd been ogling
my daughter volunteered his jump starter, which got me going again. I
suppose I'll put the charger on the battery while it sits in the
driveway overnight before trips.

Do you have two batteries? That's the best way of solving the
"accessory run down" problem. One battery for engine starting only,
the second battery for accessories only, using a "combiner" to keep
the accessory battery charged.

A combiner is an automatic switching relay that senses the voltage of
the engine start battery and connects both batteries together if
higher than a predetermined level, usuall 13.5 volts or thereabouts.

http://www.jamestowndistributors.com/userportal/show_product.do?pid=51850&BASE