Deep Discharge AGM and High Amp Charging Experiences

[mobiledynamics]

Just curious.....what has your experience been with deep discharging AGM and High Amp (20+) Charge Cycles.
How low have you taken it.....love to hear experiences on how low, and how ~long~ it was low till you gave it a charge.

It's interesting as I spoke to 2 High/Higher End AGM manuf. recently as one of them recommended the High Amp Charge, and the latter told me, if I had the ~time~, traditional low and slow is always best. Even when deeply discharged.

 

[chromisdesigns]

Top quality AGM cells can accept bulk charge rates up to half of the Amp Hour rating, up to about 85% charged, then you need to slow down for the remaining 15%. If you have enough capacity to run in the 50-85% charged range, they will last near forever with this use regime.

You can take them down to 25% at the cost of a lot of discharge cycles.

Note we are talking Lifeline and equivalent quality batteries here. Sears AGMs will die quickly from repeated deep discharge / fast recharge cycling.

 

[228B]

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chromisdesigns
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Sears AGMs will die quickly from repeated deep discharge / fast recharge cycling.

Perhaps not, if that Sears AGM was made by Odyssey. See here. I agree with the rest of your excellent post.
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mobiledynamics
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Just curious.....what has your experience been with deep discharging AGM and High Amp (20+) Charge Cycles.
How low have you taken it.....love to hear experiences on how low, and how ~long~ it was low till you gave it a charge.

Well... a few years ago I managed to kill an expensive Odyssey/Die Hard Platinum Group 31 by accidentally taking it down to well below 7 volts and leaving it there for weeks, on three or four occasions. In the final analysis I was an idiot but there were two or three different scenarios that led to those (virtually-) dead shorts... so one could say I was three times the idiot. Hahaha... oh well.
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The battery was connected to the 2.5 to 3.1-ish amp draw from an Engel fridge that had been left running in my camp trailer which was in storage. I had thought the fridge was plugged into 120V "shore" power... I brought the battery back to full charge (but was it? The absorption phase was nowhere near long enough in hindsight...) twice but when I tried to bring the battery back a THIRD time from the depths of battery discharge hell it had been too badly damaged. I still have it (it will still power some 12V lighting but it can no longer crank a starter or deliver any other high-amp-draw load. I tried. Then I had it tested...). It sits waiting to go to a recycler where I might recoup a few dollars. 75 lbs of "99.99% pure virgin lead" has to be worth more than $20. Hahaha... maybe I'm wrong.
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NOW THEN:
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In the interim I've paid close attention to how a good AGM should be treated, and purchased another Group 31 100Ah Odyssey DHP, an EnerSys/Odyssey OMAX-50A-1B charger (not cheap) then I discovered this nice Odyssey battery tech PDF regarding the Odyssey and it's unusual characteristics... "unusual" being that no other battery suitable for deep-discharge duty claims to also be able to deliver the amperage (without harm) to see service cranking an engine starter.
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Odyssey claims that one could (but I'm not gonna! ...at least, deliberately, anyway. I'm using a 50% depth of discharge guideline, now) see 400 cycles to 80% Depth of Discharge! Hey, that's nice to know, but however low the battery gets we need to AS SOON AS HUMANLY POSSIBLE, re-charge that thing immediately, and with as many! amps as you can give it. In the case of this Odyssey charger, that's up to 50 amps during the "bulk" charge phase... when this battery is being recharged using solar, however, the most it sees in bulk is 12.5 amps (not volts).
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More important is that this particular AGM battery sees up to 14.7 volts and for four to six hours for absorption... and then ending with the continual "float" charge of 13.6 volts... I now have my solar charge controller adjusted (Morningstar SunSaver MPPT 15-L) to these voltage setpoints and along with the EnerSys/Odyssey OMAX charger (when "shore" power is available), I finally feel that I'm taking good care of this great battery.
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mobiledynamics
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It's interesting as I spoke to 2 High/Higher End AGM manuf. recently as one of them recommended the High Amp Charge, and the latter told me, if I had the ~time~, traditional low and slow is always best. Even when deeply discharged.

With the Odyssey, anyway, it's both: hit it with a lot of amps during bulk phase charging (up to +/- 80% state of charge), then increase the charge voltage, limit the charge current and give it a lot of time for absorption.
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I have confidence in Odyssey AGM batteries. I like that they're sealed, VRLA batteries. I've learned my lesson, I now know how to treat them so I see little need to use any other brand of battery. I should add here, however, that if no Odyssey battery were available I would without hesitation gladly invest in Lifeline AGM batteries.
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Again, here's the PDF in which your questions are answered See Pages 10, 11 and 12.
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And before someone else tries to rip on the Odyssey, I'm not trying to sell anyone anything. I've only paid the price for my stupidity and beat a great battery to death on more than one occasion and am posting my sad story here. :sombrero:

 

[comptiger5000]

The Duracell (East Penn) AGM in my Jeep got one heck of a fast charge cycle this past winter. A relay stuck on for my aux reverse lights without me noticing when I parked (it was daytime) and it sat like that for about 6 hours. Came out to a battery too low to even latch the interior lights relay on.

Figured out what happened and let it settle for a few minutes while a friend headed over. Battery was resting around 9 volts. Jumped the motor and took it for a drive, keeping it down a gear to keep the revs up a bit (voltage would start to dip once I got below about 1800 rpm with the battery that low.

After about 30 - 40 minutes of driving, I brought it home and threw it on a charger. Charger went to absorb after only a few minutes (bulk charge was pretty much done in under an hour :Wow1: ). When I parked it and popped the hood, the battery was noticeably warm, but not hot (probably about 100 - 110* case temp, it was about 10* outside). Alternator was very toasty, as expected.

Battery is still going strong 6 months later, no signs of that having damaged it (or the alternator).

 

[mobiledynamics]

I suspect due to the low resistance of these pure lead batteries...that is what it allows them to take the high amp charge.
Heat kills batteries.
That's a fact.
Volt causes heat.
Anyhow, Odyssey calls for high amp bulk and Northstar, per the rep I was speaking with, told me, the high amps won't kill it....but low and slow is what they recommend.

U can take a wet cell.....hit it with high voltage to let it desulphate...
With these sealed AGM's, is the higher amp. the means to desulphate without going past 14.7
Will it create pockets between the plates, etc

I've yet to hit it with a high amp charge....I have a schumacher that will do 70 amps....in fear of toasting the battery.
I do charge it with our Cteks 7 Amp, and even if not in use, will top it off every once in a blue moon to mitigate shallow charge cycles

 

[pexic]

Hello mobiledynamics

You may take some time for reading this: http://www.bruceschwab.com/uploads/li-vs-la.pdf maybe it helps.