>>  I charged the aux battery with
>> > no load on it (fridge and inverter are the only things wired to it) for
>> > about 45 minutes to get to 12.30 volts.
> 12.3V is not a charged battery in the first place. That is approaching
> 60% discharged, depending on your meter's accuracy.
>> > In an hour and a half of using the
>> > fridge it dropped from 12.3 to 10.62 volts, about the lower limit for any
>> > cooling.

Just a reminder to keep temperature in mind--as it affects battery
charge and voltage.   See, for example:
http://www.trojan-battery.com/Tech-Support/BatteryMaintenance/Charging.aspx
and note paragraph 6.  You can probabaly ignore temperature in
the summer, but certanly not in cool and cold weather.
Another site:
http://www.odysseybatteries.com/files/techbook.pdf

Richard
Bouler