When I got my last set of batteries (150aH AGM, used), they had been tested on a high-amp car tester. But my friend who knows batteries pretty well said that was not a proper test, that what we should do was put a 25 amp load on, and see how long the battery took to get down to 11v or so. This method caused us to reject several batteries that had tested fine on the high amp tester. And the batteries I got have been good.This same friend, though, told me it was important to cycle batteries in long term storage (not just float them). Doing that, with the 25 amp load, one got away from me, suddenly dropped to 10.5v or so, and that killed it.I have also killed numerous 33aH batteries by putting a 100amp brief load on them, before I figured out that was not cool.So. How should I test these used AGMs I am looking at now? Should I rely on the sellers 150aH 15-second test? Should I do a smaller load for longer? What do you all do?

You need a known resistive load like ganged resistors, i.e. one that has been measured. For a 150AH battery, a 20 A load would be good. The load is connected and with timed duration. The battery is then measured for voltage, which indicates SOC. I don't know how you'll be able to do this at a battery reseller's shop. They are probably not going to allow it. Your choice would then be to buy one, test it and then purchase more. I think most purchasers take the word of the seller but there would be nothing wrong with checking voltage before purchase. A higher DC voltage would indicate that the batteries have been treated well.FWIW, I am using three small AGM telecom back-up batteries that were pulled for scheduled replacement. They work just as advertized.

According to our Interstate Battery rep, regular battery testers will not test AGM batteries. Interstate, at their warehouse has a $1500 tester they use. We opted to not spend $1500 for a tester we would rarely use. We have $500 Snap On resistance type tester with print outs and it will not work on AGM batteries. Doug

Sounds like good advice from your friend. The car battery tester is checking for cranking amps, which is all a car cares about. As RV'ers we care about the so-called "20 hour rate", providing a smaller current over a longer period.Not to discount surge capacity to much though, especially if you plan to use an inverter. It might need to pull 1500 watts or more from the batteries briefly, and that's closer to cranking amps than the 20 hour rate.

In all honesty, I don't think too many of us buy used batteries. At least I've never seen anyone mention "new to me" batteries.

GordonThree wrote:Sounds like good advice from your friend. WHAT ?? Most of his advice is dead wrong.....like the part about having to discharge them down to 11 volts for a test. The OP has already seen what that can do. And the part about cycling being better than a proper float during storage is just total bunk.A "standard" load test will tell you about the basic health of an AGM battery......as measured by the same spec's as a conventional wet cell. Odds are extremely high that if it passes that test there is little or nothing wrong with it that would interfere with normal use.Being obsessive about things like this often leads you to buy into obscure theories that often have no practical use.....even if they are technically "right".P.S. Some conventional wet cells can pass a high current load test when they are on the verge of total failure too. If the symptoms make you think they are about at the end of their useful life, then the odds are extremely high that they really ARE.

Testing AGM batteries? | Good Sam Community

MrWizard
Moderator
Jun 06, 2016
Same ones,
But seems like the 20 hour rate should be higher than that
pianotuna
Nomad III
Jun 06, 2016
Hi,

If these are the ones Naio purchased the 20 hour rate is 135 amp-hours.
MrWizard
Moderator
Jun 06, 2016
A little note on specs

Camping world sells exide
The Edge agm dual purpose sells for $199 and are spected at 120 minutes RC at 25 amps

The 12flx500 batteries I bought
Spec at 48 amps for 120 minutes
And
22 amps for 300 minutes
15 amps for 480 minutes that's 8 hours

An 8 hour capacity of 119 amp hrs , 8 hours discharge not 20 hours
The 20 Hr capacity will be much higher, anyone know how to calculate/extrapolate that from this info

Float voltage is 13.62 at 77°F
Charge voltage and amps is 'undeclared'

Hoping to get these installed today
Naio
Explorer II
Jun 05, 2016
Oh, that's great, Mr Wizard :).
westend
Explorer
Jun 05, 2016
....... I have a beer budget with champagne tastes. I need my batteries to last a long long time.

I hear that!:C
pianotuna
Nomad III
Jun 05, 2016
Hi,

If possible on a vrla you do not wish to charge passed the gassing voltage by much, or for very long. Surplus acid AGM's are a different beast than what you have, so probably different guide lines would be best. I am a neophyte as well, and I have a beer budget with champagne tastes. I need my batteries to last a long long time.

westend wrote:
Hey Don,
I'm rather a neophyte with VRLA construction but I would think the recombinant gas mechanism would reduce the need for a lot of gassing, irrespective of SG. I might be totally wrong about that?

The Genesis EP AGM's I'm using describe a "reconditioning" process should the batteries lose capacity. IIRC, the voltage is set at 16V for a period of time and there is no admonition about temperature. That's not a real healthy diet IMO. as boiling out any electrolyte would be bad AFAIK.

FWIW, my 6 V bank has the temp compensation connected from the solar controller and that pair is fairing very well. I just recently added water to the cells after a year of nearly constant charging. My controller is set to go into 14.6 bulk for a short period and then floats for the rest of the day if voltages stay above 13.5 V. The SG remains at a baseline 1.30 while in storage.
MrWizard
Moderator
Jun 04, 2016
I bought 4 of these for the house side to replace my 5 yrs old set
Everyone i bought checked at 13+ volts
I grabbed one of my picks , put my 500 amp carbon pile tester on it
And it tested at 300 amps load

I think i will be just as happy with these as with my CD technologies set
westend
Explorer
Jun 04, 2016
Hey Don,
I'm rather a neophyte with VRLA construction but I would think the recombinant gas mechanism would reduce the need for a lot of gassing, irrespective of SG. I might be totally wrong about that?

The Genesis EP AGM's I'm using describe a "reconditioning" process should the batteries lose capacity. IIRC, the voltage is set at 16V for a period of time and there is no admonition about temperature. That's not a real healthy diet IMO. as boiling out any electrolyte would be bad AFAIK.

FWIW, my 6 V bank has the temp compensation connected from the solar controller and that pair is fairing very well. I just recently added water to the cells after a year of nearly constant charging. My controller is set to go into 14.6 bulk for a short period and then floats for the rest of the day if voltages stay above 13.5 V. The SG remains at a baseline 1.30 while in storage.
pianotuna
Nomad III
Jun 04, 2016
Hi,

The reason I asked is because my surplus acid agm telcom jars have a specific gravity of 1.30 when fully charged.

I know that tropicalized electrolyte is of a lower specific gravity and winterized electrolyte is a higher specific gravity. I don't know the actual numbers.

Now that I think about it--clearly the temperatures for gassing need to be lower with the higher specific gravity. That is kind of important with any VRLA jar.
westend
Explorer
Jun 04, 2016
pianotuna wrote:
Does anyone know if a higher specific gravity increases temperature for charging rates?

Example:

1.275 vs 1.30 can temperature be higher for the 2nd number when charging?
Good question and could get quite theoretical/technical in answering. One unknown is: Are both of the specific gravity densities you listed at the full SOC measured density?

Off hand, I'd say no, it doesn't matter because there is a gain in density while charging and all other things being equal, the rise in density range may be the same for both examples, hence temperature would be monitored alike.

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