In addition, you're not adequately charging your battery. Is your
converter ("recharger") properly set up? Is there a selector switch to
designate wet cell vs. AGM?

If I remember this correctly, I have setup the charger to the correct
battery type that is "wet cells". I will double check when I go home
anyway just to be sure.

You battery voltage should reach 2.2 volts per cell while recharging
(2.2 times 6 equals
13.2) and should still read at least 2.1 volts per cell (12.6) hours or
even days later if there isn't a load on the battery. If your charger
shuts off at 12.99 volts, instead of 13.2, you are slightly
undercharging your batteries.

Yes, you are probably right. The boating book also says that I should
see the voltage above 13-volt (I don't remember the exact number).
What's the significance of slightly under-charging the batteries? Does
the charger undercharge the batteries to avoid boiling the batteries?

Obviously you had the key on when monitoring the voltmeter. You may
have something drawing current through the ignition switch that isn't
occuring to you. (If simply running the guages and dash lights is
drawing you battery down that quickly, you need a new battery).

I don't think there is anything else that is drawing power from the
batteries other than the gauges and the dash lights. The boat doesn't
have any fancy electronic device other than the gauges (voltmeter, rpm
meter, motor temp gauge) and a bilge pump that doesn't seem to be
working.

I hope the batteries are fine. I did a load test on the batteries
using the electric starter of the motor as a load. And the batteries
were fine. Honestly, I don't know how old the batteries are. I will
have to do a load test on the batteries one more time when I
recommission the boat in the spring.

If you're seeing 11 volts with the engine *running* and it isn't a
corroded connection, etc, you would want to take a close look at the
alternator.

Actually, I saw the voltmeter showing something like 12.7-volt or above
when I was running the motor. This means the alternator was running
fine.

What this means is that I should make sure the connection between the
batteries and the voltmeter is fine in order to establish a good base
line before I do anything else (anything else means things like doing a
load test on the batteries, like checking the voltage when the
alternator is checking). Otherwise, any number that I get from the
voltmeter is questionable.

Jay Chan