There are a number of different ways to attack this problem. Here are
the ones I'd use:

1. Fully charge the batteries and leave them completely disconnected
for a few days. Then check the voltage (or specific gravity using a
hydrometer) to see if they're still charged. This will tell you if one
or both of the batteries are dead. If you don't have a voltmeter you
can pick up a cheap one at radio shack for $15 that will be accurate
enough to tell you if you have problem.

2. Get an ammeter and check each wire to see if there's any load on the
batteries. We have one on our electrical panel and I always use it as
my final check to make sure that nothing is drawing power before I
leave the boat. Or if you don't have or want to buy an ammeter
disconnect all devices and methodically reconnect them (1 each day) to
see if there's a problem there.

3. If 1 and 2 still don't give you an answer I'd suspect a short or a
mis-wiring of the batteries.

This is obvious but if batteries are lead acid make sure the water
level is high enough that it's covering the plates. On our house bank I
have to add water to the batteries about 4 times a year.

My dad had the same problem your describing on his power boat and when
I started digging around the house bank I discovered that the boatyard
had mis-wired the batteries when they reconnected them in the spring so
that the alternator wasn't recharging the batteries.

-Todd

Free boat blogs: http://boatblogger.com

William G. Andersen wrote:
How do I find what's draining the power on my battery?