Testing AGM batteries?

[Naio]

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?

[MrWizard]

The only probe I have says 95.3°f on the side center of battery case
Felt cool to my touch, cooler than me

Down to 300ma at 13.4v

[pianotuna]

Hi MrWizard,

So long as you don't get the batteries too hot. I.e keep them below 50 C (122 f).

MrWizard wrote:
Yeah yeah better to do the controlled over charge in the cold weather
In cold weather I don't need to run the a/C and generator all day
Right now.. The amp meter is showing 1.6 amps at 13.39v ambient temp 88°f
This from a 70 amp PD with charge wizard
In this weather I do not kick it up to boost mode

[MEXICOWANDERER]

Heh heh heh...

Do a plot graph...

Voltage - amperage - time

Most Revealing

[MrWizard]

When using the generator only for charging, not cooking etc
Like after supper
I Will generally stop at 2 amps per battery, 8 amps on the display
But when using the A/C I just let it charge even when down to 0.5 amps per battery
Often this is when I will kick on the recondition or desulfate mode of the B&D charger
Bay doors are open and usually parked in shade
There is no sign of bulging on my CD tech batteries
Yeah yeah better to do the controlled over charge in the cold weather
In cold weather I don't need to run the a/C and generator all day
Right now.. The amp meter is showing 1.6 amps at 13.39v ambient temp 88°f
This from a 70 amp PD with charge wizard
In this weather I do not kick it up to boost mode

[pianotuna]

I'm looking at a chart from http://www.cdtechno.com/pdf/ref/41_2128_0212.pdf

It appears that charging rate starts at c/4, tapers to c/8 at about 90% and c/16 at 100%, then c/32 at 110% and finally c/64 at 115% of capacity.

So the 139 amp-hour battery would be 34.75 amps (I won't do this myself, but will stick to c/5), 90%; 17.375 amps, 100%; 8.6875 amps, 110%; 4.34375 amps, 115%; 2.171 amps.

[westend]

Landy,
My Enersys Genesis EP telecom batteries list charging voltages for cycled use at 14.4->15.7. Current limit--none.

The discontinued owner's manual had a section on charging where they did some outlandish experiment using really high current (220 A ?) for a long duration (150 hrs?) and the battery tested fine after that. Don't know how long it took to cool down to handle it, though.

[landyacht318]

I judge battery performance with an AH counter often rezeroed when it is known the battery is indeed full as full can be, and voltage held for AH removed under a certain load and a big helping of trends and tendencies.

My current AGM is still causing some head scratching, as in November it will be 3 years old. It has about 350 deep cycles on it anbd a couple hundred more shallow cycles, and a few thousand engine starts on it, yet under discharge it is maintaining the same voltages under the same loading as it did when new but I rarely take it below 50%, and Mex once said this is where the lost capacity will be much more noticeable, voltage held wise.

Its degradation has only been noticeable in that it has lost some of that supremely violent quick engine cranking ability, and when new it could easily suck 100+ amps at ~50% depletion, now absorption voltage can be reached at ~75 to 80 amps at 50% depleted.

It is a 90AH group 27 Northstar AGM, and it continues to impress me. But it needs that high amp recharge applied from its most depleted state every so many deep cycles or performance tanks noticeably on cycle number 4 or 5 of low and slow solar only recharge to full.

Too many deep cycles without a high amp recharge and then it requires less than 50 amps to reach absorption voltage almost immediately and amps begin tapering almost immediately, and then it takes forever for amps to taper to 0.5% of capacity at absorption voltage.
So too much low and slow recharging after back to back deep cycles means much longer recharge times and increasingly so, even if a stronger amperage charger is used.

While the lesser $$ AGMS say no more than 30% charge rate, I believe they will still benefit from charge rates up to this level. My Northstar, like Odyssey and Lifeline AGM have no really easily achievable upper limit on charging amps, and My Northstar appear to be happier than a pig in feces whenever I can feed it 40+ amps from 50% to absorption voltage.

Holding absorption voltage until amps taper to 0.5% of capacity is just as important, but both the high amp and the taper to 0.5% of capacity at absorption voltage is the key to maintaining performance, In my experience with it, with a AH counting battery monitor at my right hand and an interest in the subject, and the desire to experiment and see the results.

The surplus tellyCom AGMS seem to have some different needs than the regular Usual suspects in the AGM world, and my statements are not meant to apply to those.

[pianotuna]

If you scroll down the page there are several links about taking care and testing of vrla batteries.

http://www.cdtechno.com/resource/support_doc.html

[Almot]

Check voltage before buying.
AGM can deep cycle when in use, but they don't like being discharged below 60% while in storage.
Fully charged AGM typically has more than 12.7V, check the manual for this particular model.

[pianotuna]

Hi 2old,

I've been using "new to me" surplus acid telcom jars for 10 months. I'm ecstatic with them. They recharge fast to a much higher percentage before they start to taper the charging rate. They will accept 27 amps each when hungry so I have deliberately throttle back my charging rate to keep to that limit of 108 amps for four jars.

I use them regularly with the Magnum hybrid inverter with the load support feature. This is especially useful when running the generator because I can run it in eco mode, saving quite a bit of fuel when I'm in the mountains.

I have seen the inverter draw 276 amps for short periods of time.

I still think that most battery banks for RV's are far too small (and I include mine in that category now at 566 amp-hours). If they ever get LI that works in the cold I'll be lining up to move over.

[Naio]

MEXICOWANDERER wrote:
Naio, download and read this PDF manual. You can trust the information.


https://www.tayna.co.uk/docs/datasheets/lifeline/lifeline-manual.pdf

Thanks Mex :B.

I see this says 25a down to 10.5v. So my battery that was killed by that, I guess it was at death's door already.

[2oldman]

Naio wrote:
2oldman, if you do a search on "telecom batteries" here you might get a few hundred hits.

I got a few pages.

I realize a few of you do this, but I don't think it's worth taking a poll. Buying used batteries is not for amateurs. Do you feel lucky?

Have we figured out how to test them yet?

[Naio]

2oldman, if you do a search on "telecom batteries" here you might get a few hundred hits.

[NinerBikes]

MrWizard wrote:
I bought 'new to me'
Service swap out agm UPS telecom batteries in 2011
Five years of hard use and they still do a nights work,
Just not as much reserve left in the morning now as then
IMO one of the very best bargains available
There are a number of members on here that have these batteries
Sometimes they call then surplus batteries

Where's the "like" button. I've saved a fortune on no more "acid wash" Levi 550's and T shirts. The savings have MORE than paid for the newer AGM battery.

Don't bother testing, when an AGM no longer covers your electrical needs, trade it in on a newer one and be done with it. Of course, don't abuse it either, keep it fully charged when not in use, and use it when you need it. If it's running out of power too soon for you, time for a newer battery or a capacity test.

[MrWizard]

I bought 'new to me'
Service swap out agm UPS telecom batteries in 2011
Five years of hard use and they still do a nights work,
Just not as much reserve left in the morning now as then
IMO one of the very best bargains available
There are a number of members on here that have these batteries
Sometimes they call then surplus batteries