On Mar 18, 8:01*am, ContestID67 wrote:
One other thought for the automated "instant" testers - While this may
indicate the Ah capacity of the battery, is that an accurate
indication of the often asked question "But, how long will it last?"
Literally, does it tell me how many minutes do I have between full
charge and my minimum voltage threshold? *There is certainly a
corrolation between Ah capacity and the duration of actual use, but is
there a formula?

Thanks once again, John DeRosa

Hi John,
I expect just about everyone that has a fancy set-up started with a
lamp, a voltmeter, and clock. It is a very accurate system at a very
low cost, I suspect more accurate than the "GOLD-PLUS Intelligent
Battery Tester". Just takes a lot longer.

Every battery has a certain Ah capacity at a given load. For example,
the 12120 battery is rated to deliver 1 amp for 14 hours (not all
batteries have such a lovely symmetry to their spec) and is rated to
deliver 24 amps for 12 minutes and 2.4 amps for 4 hours. Having a
discharge curve is useful. Looking at that curve I see the battery
will provide your load of .6 amps for about 17 hours. I have a
transponder, two varios one of which has an illuminated display, a
very bright LX Minimap, and still keep everything to .85 amp. So
according to that curve I'll get 10 or 12 hours from a new battery,
less as it gets cold or old. I plan to acquire a 12150 (15 Ah) and
also have a 2.4 Ah back-up I can switch to.

Is that what you were asking about as far as a formula? Really I
think you want to match the load (light bulb) to be as close to your
glider load as you can, or a little more. Then the length of your
test will be the same as the duration of your battery in flight. The
other consideration is that your battery will last much longer if you
don't discharge it all the to flat very often. In theory you could
take a 12120 and never fly it down past 12 volts and it would last
quite a few years.

Brian