HI folks,
I've been struggling with how to determine how much life is left in my AGM
batteries. The classic test that a battery shop does is a "load test", but
I had heard that such a test was not very meaningful for deep cycle
batteries. Some test of AH capacity needs to be done. But I was never sure
how to do it until recently. Now that I have a method, I've tested all all
the batteries I have (both the ones I was using and a group of used ones I
purchased recently) and thought you might like to see the numbers.
First I did a standard load test on all of them as determined in my Load
Tester manual (3X the AH rating (330 Amps in this case) for 15 seconds)
using the device below:
http://www.harborfreight.com/500-amp-carbon-pile-load-tester-91129.html
I then recharged each battery fully with my 12V smart charger
http://www.battery-rechargeable-charger.com/vector-VEC1095A-car-battery-charger.htmlusing
the AGM profile.
I followed that by doing an AH capacity test using the procedure shown here:
http://www.instructables.com/id/AmpHourTest/
I bought a 400W inverter at Home Depot, bought an old plug in mechanical
clock for $5 on Ebay, and used a 75W incandesent bulb which meant the load
was at least 6.25 amps. I'm not sure how much current the old clock was
drawing (probably not much). Even if the clock drew noticable current, that
would mean a higher total draw and thus the AH results would be somewhat
better than I found. But those AH values here are "at least" that much.
You can argue with the specifics of these procedures - they may not be the
most accurate way to do this, BUT the numbers are "RELATIVELY VALID" since I
did the same thing to all the batteries both times.
The batteries are 12V AGMs (110 AH rated)
http://www.mrsolar.com/pdf/universal_battery/UB121100.pdf They are sealed
so doing specific gravity testing of the acid is NOT possible and I
understand that would only get me SOC anyway and not AH capacity.
Here's what I found: .
Group 1: Pack I was using - they were dying and I was starting to replace
some, but I basically killed them by pushing them well below 20% several
times (yes, David I committed battricide). I had to be towed home a couple
of times and the last time my wife pushed my home the last mile with our
Honda Civic. Have not driven the car since then. The very small AH numbers
for this group don't really surprise me under the circumstances. The car sat
for a week or so, but I had done a full charge of the pack as soon as I had
gotten home. Then a few days before I did the testing I did a 3 hour
equalization charge using my 120V Quick Charge Select-A-Charge (110V input;
10 Amp max). All were resting at about 13.2-13.3V each before the tests.
Cycles on the battery Load test voltage AH capacity
60 ** 10.2V 33
60 ** 10.0V 16
120 10.6V 3
350 10.6V 3
120 10.7V 3
350 10.8V 5
60 ** 9.2V 4
350 9.6V 3
10 ** 9.8V 12
350 10.4V 3
Group 2: Others (not yet used by me). I had charged them all about a week
earlier one at a time using my 12V smart charger. They were resting about
about 13.0-13.1V each. before the tests.
Cycles on the battery Load test voltage AH capacity
** 9.0V 39
** 8.9V 53
** 9.4V 51
** 9.4V 47
** 9.6V 51
** 9.1V 54
** 9.2V 50
** 10.0V 57
** 9.6V 53
** 9.6V 53
** 8.8V 51
** had previously been used as part of a UPS standy system, but I really
don't know how much use they've had (i.e., how hard they were pushed or how
often they were cycled).
It's hard to argue with these data. Bottom line is that CLEARLY THERE IS NO
RELATIONSHIP BETWEEN THE TWO SETS OF FINDINGS. There doesn't seem to be much
correlation between load test results and AH capacity testing. This may not
be news to some of you but it was to me. I'm glad I went to the trouble and
I now have the ability to test AH capacity.
Given what we want to use the batteries for (deep cycling), and what I know
about the history of these batteries, I'm much more inclined to trust the AH
capacity numbers. My sense is that doing a conventional load test MAY tell
you if a battery is really bad (it didn't here; all of the above voltages
were a "pass" on the load tester), but it doesn't seem to really tell you if
a deep cycle battery is any good for deep cycling.
I now plan to install the 10 best of the "others" shortly (those with 47-57
AH still in them) and see how they do.
Peter Flipsen Jr
Meridian, ID
http://www.evalbum.com/1974
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I've been struggling with how to determine how much life is left in my AGM
batteries. The classic test that a battery shop does is a "load test", but
I had heard that such a test was not very meaningful for deep cycle
batteries. Some test of AH capacity needs to be done. But I was never sure
how to do it until recently. Now that I have a method, I've tested all all
the batteries I have (both the ones I was using and a group of used ones I
purchased recently) and thought you might like to see the numbers.
First I did a standard load test on all of them as determined in my Load
Tester manual (3X the AH rating (330 Amps in this case) for 15 seconds)
using the device below:
http://www.harborfreight.com/500-amp-carbon-pile-load-tester-91129.html
I then recharged each battery fully with my 12V smart charger
http://www.battery-rechargeable-charger.com/vector-VEC1095A-car-battery-charger.htmlusing
the AGM profile.
I followed that by doing an AH capacity test using the procedure shown here:
http://www.instructables.com/id/AmpHourTest/
I bought a 400W inverter at Home Depot, bought an old plug in mechanical
clock for $5 on Ebay, and used a 75W incandesent bulb which meant the load
was at least 6.25 amps. I'm not sure how much current the old clock was
drawing (probably not much). Even if the clock drew noticable current, that
would mean a higher total draw and thus the AH results would be somewhat
better than I found. But those AH values here are "at least" that much.
You can argue with the specifics of these procedures - they may not be the
most accurate way to do this, BUT the numbers are "RELATIVELY VALID" since I
did the same thing to all the batteries both times.
The batteries are 12V AGMs (110 AH rated)
http://www.mrsolar.com/pdf/universal_battery/UB121100.pdf They are sealed
so doing specific gravity testing of the acid is NOT possible and I
understand that would only get me SOC anyway and not AH capacity.
Here's what I found: .
Group 1: Pack I was using - they were dying and I was starting to replace
some, but I basically killed them by pushing them well below 20% several
times (yes, David I committed battricide). I had to be towed home a couple
of times and the last time my wife pushed my home the last mile with our
Honda Civic. Have not driven the car since then. The very small AH numbers
for this group don't really surprise me under the circumstances. The car sat
for a week or so, but I had done a full charge of the pack as soon as I had
gotten home. Then a few days before I did the testing I did a 3 hour
equalization charge using my 120V Quick Charge Select-A-Charge (110V input;
10 Amp max). All were resting at about 13.2-13.3V each before the tests.
Cycles on the battery Load test voltage AH capacity
60 ** 10.2V 33
60 ** 10.0V 16
120 10.6V 3
350 10.6V 3
120 10.7V 3
350 10.8V 5
60 ** 9.2V 4
350 9.6V 3
10 ** 9.8V 12
350 10.4V 3
Group 2: Others (not yet used by me). I had charged them all about a week
earlier one at a time using my 12V smart charger. They were resting about
about 13.0-13.1V each. before the tests.
Cycles on the battery Load test voltage AH capacity
** 9.0V 39
** 8.9V 53
** 9.4V 51
** 9.4V 47
** 9.6V 51
** 9.1V 54
** 9.2V 50
** 10.0V 57
** 9.6V 53
** 9.6V 53
** 8.8V 51
** had previously been used as part of a UPS standy system, but I really
don't know how much use they've had (i.e., how hard they were pushed or how
often they were cycled).
It's hard to argue with these data. Bottom line is that CLEARLY THERE IS NO
RELATIONSHIP BETWEEN THE TWO SETS OF FINDINGS. There doesn't seem to be much
correlation between load test results and AH capacity testing. This may not
be news to some of you but it was to me. I'm glad I went to the trouble and
I now have the ability to test AH capacity.
Given what we want to use the batteries for (deep cycling), and what I know
about the history of these batteries, I'm much more inclined to trust the AH
capacity numbers. My sense is that doing a conventional load test MAY tell
you if a battery is really bad (it didn't here; all of the above voltages
were a "pass" on the load tester), but it doesn't seem to really tell you if
a deep cycle battery is any good for deep cycling.
I now plan to install the 10 best of the "others" shortly (those with 47-57
AH still in them) and see how they do.
Peter Flipsen Jr
Meridian, ID
http://www.evalbum.com/1974
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