"Charles T. Low" wrote in message
...
Doug,

Thanks, very helpful.

So, does this seem valid to you? - An accurate voltage reading is a good
indicator of a battery's condition, but specific gravity is better,

Yes. But only after the battery has rested under zero load for a while.

and a
slow load test (to 50%) is the best?

A slow load test tells the current capacity of the battery which is what the
battery is being asked to do.

Or are they testing different things,
all of which are important?

Perhaps. I suppost that if you are using the same battery bank for
house and starting, then multiple types of test may be informative.
But for a house bank a slow realistic load test gives the bottom line.
Voltage and SG tests are really telling the current instantaneous state
of the battery. That does not necessarily relate directly to the expected
perfromance under load. One is static the other is dynamic.

Could it do well on a load test without good
voltage or sg's?

I don't see how.

And, what use is a commercial load tester, then? Why do they make them?

To test the high current delivery performance of starting batteries as best
I can tell.

Is
it better than an sg but not as good as a slow load test?

As I said earlier. These are testing different things. SG gives the
current state of the battery, a slow load test tells the capacity of the
battery. A reasonable analogy might be, the amount of fuel you have
in your fuel tank as apposed to how far that fuel will get you at a
given speed. You can measure how much fuel you have by weight or
by volume or by level, but that will not tell you how far you can go
at 10 mph vs 100 mph. The condition of the engine enters into the
equation as well just as the condition of the battery does.

Thanks again. Charles

P.S. I corrected the spelling of "betteries" - couldn't take it any more!

====

Charles T. Low
- remove "UN"
www.boatdocking.com
www.ctlow.ca/Trojan26 - my boat

====

"Doug Dotson" wrote in message
...
The discharge time of a deep cycle battery is influenced by many
things other than SG. The condition of the plates etc all come into
play. While one may be able to draw heavy current for a brief
period that does not necessarily translate into good low power
performance. A long term low current test tells the actual story
since it is how the battery is being used in normal use. The SG
gives the state of charge from a theoretical sense as does the voltage.