Great tips Bill. Thanks.

I *finally* found a receipt for the battery.  It's a "12V 45AH Sealed
Battery". I called the vendor and found out it's an AGM battery.

It's holding it's charge longer. 2 hours with DVD player via the
inverter and it went down to ~60%.

The bulb load test makes sense and is a good tip, but I really should
learn how to use my digital VOM to test current draw. I know that one
should use hard numbers to measure things.

Cheers,

Neil.

On Thu, Sep 4, 2008 at 8:44 AM, Bill Prats <b.bill.p@gmail.com> wrote:
>>  3. Did I hurt my Aux Battery?
>
> I have a large ham radio and have lots of battery experience, some of the
> brands don't last more than a few years.  Here is any easy way to test the
> capacity of a smallish battery.  Wire a tail light across it by itself and
> time how long the light burns a decent glow.  Since the wattage is on the
> bulb you will get a good idea about the condition of the battery.  Power in
> Watts = Voltage times current.  6 watt bulb on 12 volts draws a 1/2 amp, 12
> watt lamp on 12 volts draws 1 amp.  24 watt lamp on 12 volt draws 2 amps.
> A 100 watt sound system full on will draw around 9 amps and more depending
> on other features and volume level.  A older 40 amp hour battery might be
> good for 2 hours in my opinion.
>
> Try not not to drain any battery below 11.5 volts, that level varies by
> battery but its generally accepted as the bare minimum before the battery
> plates warp and short together, bad news.
>
> Its possible the battery is ageing and the sound system draws far more power
> than estimated.  Put an amp meter in series with the system to measure.
>
> The only sure way to find out the battery chemistry type is to research the
> brand/model number. Sometimes a deep cycle/gell or AGM will weigh a few
> pounds more than it automotive type cousin.  Well at least you get a rough
> idea.  I have the same problem, a 55 amp battery that weighs a ton.
>