Geza Polony wrote:
>  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.
>
You discharged your battery 100%. Not recommended, and only a solid,
true deep cycle battery is going to allow you to get away with that,
once, maybe twice. 50% is about all you should do to a marine, or psuedo
deep cycle. Trojans and other true DCs, can be pushed to 80% discharged
a few times without serious long term damage. In addition, when you hit
100% discharge, you will never get it back to 100% of capacity with a
vehicle alternator.

> Dennis, if 800 watts at 120 volts fried the battery--then what the h**l do
> they sell 1200 watt inverters for?

People like me, who have 12 batteries in the garage, running the
inverters in my house :-)  Of course, that requires some rather high
quality inverters in the first place, and not the kind that they sell at
Pep Boys or Home Depot <g>

I am just an interested observer in this thread, but it needs to be
pointed out, and I may have missed it having been said, that if you
invest in true deep cycle batteries, and don't use a three stage charger
to keep them topped off, you are not getting the max life out of it, and
in fact, are never getting it "filled up" in the first place. It may say
100aH, but without the proper charge rates and controlled currents, you
won't see those numbers in real life. These are not 'starter' batteries,
and are not made to be bulk charged, with a constant dump of current.

Just wanted to point that out....Dennis knows of what he speaks. Those
who are paying for true deep cycle batteries, who want to take care of
their investments, and get the most out of them, would do well to do
some web work, and get the details on how to best take care of them.

HTH,

John