"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

====

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...)

====

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

====

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, and a
slow load test (to 50%) is the best? Or are they testing different things,
all of which are important? Could it do well on a load test without good
voltage or sg's?

And, what use is a commercial load tester, then? Why do they make them? Is
it better than an sg but not as good as a slow load test?

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.

"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.

Thanks, Doug, and also to Argonauta, and to Larry W4CSC. (Some of the
information conflicts, but that's not the first time that's happened!)

So, to summarize:

-voltage and sg measure charge but not capacity;
-commercial load testers might be for testing starter batteries, esp. if
something is wrong and you're trying to figure out what;
-slow load testing makes more sense for deep cycles functioning in that
role.

(Of course, Darden's site says that 200 deep discharge cycles is a good
battery's life span - so if you test it, have you used up one?)

(Larry: It also gives charge/voltage tables, which suggest that you _can_
measure charge quite accurately from resting voltage - but I am prepared to
believe in more accurate types of measurement than this.)

By the way, I happen to know that a battery can have high-normal resting
voltage and be completely useless, as this thread asserts: no current draw
from it, but basement sg's - this happened to me last summer. Perhaps I
hadn't rested it, after attempted charging, nor removed the surface charge.

Charles

====

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

====

"Doug Dotson" wrote in message
...

"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.

(Of course, Darden's site says that 200 deep discharge cycles is a good
battery's life span - so if you test it, have you used up one?)

True, but a deep discharge is something that shouldn't be done in
normal practice. IMHO a 50% discharge is sufficient to get a pretty
good idea of capacity. Especially since a 50% discharge is what is
done in normal use.

Doug
s/v Callista

(Of course, Darden's site says that 200 deep discharge cycles is a good
battery's life span - so if you test it, have you used up one?)

True, but a deep discharge is something that shouldn't be done in
normal practice. IMHO a 50% discharge is sufficient to get a pretty
good idea of capacity. Especially since a 50% discharge is what is
done in normal use.

Doug
s/v Callista

Thanks, Doug, and also to Argonauta, and to Larry W4CSC. (Some of the
information conflicts, but that's not the first time that's happened!)

So, to summarize:

-voltage and sg measure charge but not capacity;
-commercial load testers might be for testing starter batteries, esp. if
something is wrong and you're trying to figure out what;
-slow load testing makes more sense for deep cycles functioning in that
role.

(Of course, Darden's site says that 200 deep discharge cycles is a good
battery's life span - so if you test it, have you used up one?)

(Larry: It also gives charge/voltage tables, which suggest that you _can_
measure charge quite accurately from resting voltage - but I am prepared to
believe in more accurate types of measurement than this.)

By the way, I happen to know that a battery can have high-normal resting
voltage and be completely useless, as this thread asserts: no current draw
from it, but basement sg's - this happened to me last summer. Perhaps I
hadn't rested it, after attempted charging, nor removed the surface charge.

Charles

====

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

====

"Doug Dotson" wrote in message
...

"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.

"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.

Assuming the battery is in good condition, the open circuit voltage can
be a fair indicator of the charge of a battery if it has been rested and
the surface charge removed.

The specific gravity is a better indicator of charge, but again, the
battery must be in good condition.

In either the SG or the voltage test, a damaged battery may indicate
full charge, but be useless. If a plate has dropped, a battery could be
fully charged but not capable of delivering any current. If the water
is low (or in the case of 'service free' batteries, it is common for the
water to get so low that it just barely touches the bottom of the
plates), the voltage is fine, but it won't light a light bulb.

So, the third test is neccessary occasionally to check the 'health' of
the battery. This will tell you that the battery is capable of
delivering sufficient current. Then once you know you have a healthy
battery the SG or rest voltage will tell you the charge state.



Charles T. Low wrote:
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, and a
slow load test (to 50%) is the best? Or are they testing different things,
all of which are important? Could it do well on a load test without good
voltage or sg's?

And, what use is a commercial load tester, then? Why do they make them? Is
it better than an sg but not as good as a slow load test?

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.

Assuming the battery is in good condition, the open circuit voltage can
be a fair indicator of the charge of a battery if it has been rested and
the surface charge removed.

The specific gravity is a better indicator of charge, but again, the
battery must be in good condition.

In either the SG or the voltage test, a damaged battery may indicate
full charge, but be useless. If a plate has dropped, a battery could be
fully charged but not capable of delivering any current. If the water
is low (or in the case of 'service free' batteries, it is common for the
water to get so low that it just barely touches the bottom of the
plates), the voltage is fine, but it won't light a light bulb.

So, the third test is neccessary occasionally to check the 'health' of
the battery. This will tell you that the battery is capable of
delivering sufficient current. Then once you know you have a healthy
battery the SG or rest voltage will tell you the charge state.



Charles T. Low wrote:
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, and a
slow load test (to 50%) is the best? Or are they testing different things,
all of which are important? Could it do well on a load test without good
voltage or sg's?

And, what use is a commercial load tester, then? Why do they make them? Is
it better than an sg but not as good as a slow load test?

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.