"Charles T. Low" wrote in message
...
"Doug Dotson" wrote in message
...
Load testers are good for starting batteries but don't really tell much
for a deep cycle battery.
Doug - s/v Callista

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Doug,

Any idea why is this?

Is it possible to have good sg and still fail a load test? I.e., is a load
test more sensitive than sg? (I presume that sg is more specific than
measuring voltage?) Does it go like that, in terms of accuracy?:

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.

voltage
specific gravity
load testing???

Will an appliance such as a commerically bought load tester be more or
less
accurate than doing a long, slow test oneself, such as by leaving lights
on?

A load tester (at least the ones I have seen) can't tell what the
capacity of the battery is. They just give a general idea that the
battery is chemically and physically sound. I built a system a few
years ago that would discharge a battery at a specified rate and then
automatically recharge it all while monitoring. It graphically showed
the capacity of the battery. It was also useful for reconditioning and
breaking in batteries.

(And, one other poster mentioned testing down to 50% charge as more
convenient than testing to 0% charge - isn't it also true that testing to
0%
charge will ruin the battery?)

0% charge and running it all the way down are not the same. 0% discharge
is usually considered to be 10.5v. That is why I figure 50% is good enough.
50% is generally considered the lowest a battery should be discharged in
normal use so doing so will tell what the useful capacity is.

Charles

(So many questions, such limited memory capacity...)

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

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