Testing Batteries
 

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.

Testing Batteries
 

"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.

Testing Batteries
 

"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.

Testing Batteries
 

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.

Testing Batteries
 

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.

Testing Batteries
 

On Mon, 26 Jan 2004 22:12:53 -0500, "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?

No. The voltage of 6 cells depleted to 50% of charge, as low as you
should go, is nearly the same as one at 85% charge....when there is no
load. If you're not pulling a constant current through the internal
resistance of the battery, it doesn't drop until the battery is WAY
TOO DISCHARGED.

Specific gravity is the ONLY real way to monitor cell condition and %
of charge because the A-H rating of a battery CHANGES as load changes.
(Notice how the rating printed on the side of the battery is at an X
amp rate.) The more the load current, the lower the amp-hour rating
of the battery really is. But, it's specific gravity ALWAYS tells the
real story. It's just a pain in the ass to measure.....until I found
this Australian instrument I find really neat.

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?

The load tester INCLUDES that PREDICTABLE current load that pulls down
the voltage from the internal series cell resistance caused by
discharge coating the plates with insulating lead sulphate as it
discharges and a weakening acid concentration as it is used up. It is
useable as a predictor of % of charge, but not as accurate as specific
gravity.'

It is also used in troubleshooting to find that dead cell. When you
load 6 cells in series and one of them is dead, the 50A load really
draws it down hard by the 2V lost in the dead cell. It was never
intended as a charge meter, but a troubleshooting tool.


Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!

Testing Batteries
 

On Mon, 26 Jan 2004 22:12:53 -0500, "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?

No. The voltage of 6 cells depleted to 50% of charge, as low as you
should go, is nearly the same as one at 85% charge....when there is no
load. If you're not pulling a constant current through the internal
resistance of the battery, it doesn't drop until the battery is WAY
TOO DISCHARGED.

Specific gravity is the ONLY real way to monitor cell condition and %
of charge because the A-H rating of a battery CHANGES as load changes.
(Notice how the rating printed on the side of the battery is at an X
amp rate.) The more the load current, the lower the amp-hour rating
of the battery really is. But, it's specific gravity ALWAYS tells the
real story. It's just a pain in the ass to measure.....until I found
this Australian instrument I find really neat.

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?

The load tester INCLUDES that PREDICTABLE current load that pulls down
the voltage from the internal series cell resistance caused by
discharge coating the plates with insulating lead sulphate as it
discharges and a weakening acid concentration as it is used up. It is
useable as a predictor of % of charge, but not as accurate as specific
gravity.'

It is also used in troubleshooting to find that dead cell. When you
load 6 cells in series and one of them is dead, the 50A load really
draws it down hard by the 2V lost in the dead cell. It was never
intended as a charge meter, but a troubleshooting tool.


Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!

Testing Batteries
 

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.

Testing Batteries
 

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.

Testing Batteries
 

(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