Thanks for all your comments...here are some of my comments on your
comments!

"11.5 volts cut off is way too conservative"
- Probably true. But I am an engineer and being conservative is
inbred. I just don't know what devices people are using. Older
radios don't even like anything less than 12Vdc - thus the reason you
see those odd combo batteries to get to something like 13.6Vdc. Most
moden electronics can survive down to 11Vdc and lower. So 11.5 seems
like a reasonable middle ground.

"I happened to automate the process and as such it works like this. I
have a small PLC that does the work."
"Eagle Tree MicroPower V3 logger"
"http://www.actmeters.com/"
- These are all wonderful tools which I have also used. But for those
that only test a couple of batteries once a year, these systems are
something that most people cannot justify - either too expensive or
too complicated to make. My $0.02.

"testing every 10 minutes you are working kind of hard. My battery, a
12120, takes hours to run down. "
- I guess I like nice smooth curves on my graphs. ;-) Call me
crazy. And yes it takes hours. But I do this while doing my day job
(from home) so I just glance over once in a while and take a reading.
Simple. Your mileage may vary. To speed things up does using a 2x
load and then double the resulting run time make sense?

"Do you do your test in cold air to simulate high altitude, or just
room temp?"
- Room temperature. Flying in the Midwest I don't have much of a
temperature swing to worry about. Not to mention I don't have a
temperature chamber handy. But I understand your concern for the wave
flight types. A refrigerator or ice chest? Too cold? How much is a
lead-acid battery's chemistry changed by temperature? Hmmmm.

"Also in my testing this spring I ran my 17Ah battery on the tester
and replaced it after it demonstrated some unusual performance. On
the first test it ran only 300 minutes, but when I noticed it had run
only a short time I restarted the test without recharging it. It ran
500 more minutes and then quit again. I again started the test
without recharging and it went another 400 minutes."
- I have noticed that if you take a large load off of a lead-acid gel
cell battery the voltage will recover somewhat. I don't know the
chemistry to understand why. So I wonder if you battery test rig is
getting fooled into releasing the load at your trip voltage, then the
battery recovers, and you repeat the cycle. Just a thought.

"If you are replacing the 12120 battery, look at the 12140 or the
12150. Same size, heavier, and more capacity."
- Thanks for the idea. I replace a battery per year in my set of
four. Two are on charge and two are in the glider at any one time.
So during my next annual battery buying time I will keep that in
mind.

Lastly - What I am trying to do is create a system of battery testing
that everyone can use with tools that they probably have around the
house or can purchase cheaply. All you need is a pencil, paper, a few
cheap resistors and a voltmeter. What are digical voltmeters going
for these days? $10?

Thanks again,
John DeRosa