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Old 04-06-2014, 09:41 AM   #1
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Charging rates in AGM batteries

Some may remember that back in December I posted with an attempt to assess whether I had frozen my (flooded-cell) house batteries. As it turned out, they HAD frozen, and several leaked when thawed :-( . I took advantage of this to purchase a bank of AGM's (Lifeline GLP-4CT), which I have had my eye on anyway :-). Now that we are out of the prolonged deep-freeze (sort of!) here in Minnesota, it is time for me to get the new batteries off of the pallet in my garage (those things are HEAVY!), and installed into the Rig. I have 6 batteries, to be configured in a 2X3 bank to yield 12 volts at a total bank capacity of 660 Ah.

Researching the Tech. Sheets for the batteries and the inverter/charger (a Magnum Energy MS Pure Sine Wave unit - and before someone asks, yes, this unit does have a specific setting for the Lifeline AGM's), I find I am facing the following question: the manual for the inverter/charger indicates that a Bulk charging rate is typically set at a MAXIMUM of C/5 (132A in my case), with a minimum rate of C/20.

HOWEVER, the technical manual for the Lifeline batteries indicates a Bulk charge rate as follows: "The charging current during the Bulk stage should be set as high as practical ... for repetitive deep cycling,, chargers should have an output current of **at least 0.2C** (my emphasis: 0.2C being C/5) (ex. 20 Amps for a 100Ah battery). If the output current is less than this value, the cycle life of the battery may be negatively affected. ... Lifeline batteries can tolerate in-rush current levels as high as 5C (500A for a 100Ah battery)"

While the inverter/charger's manual DOES state "the C/5 or C/20 charge rate settings are guidelines ... for specific charge rate requirements, refer to your battery manufacturer.". I was aware that AGM's are able to tolerate faster charge times, but this is a HUGE discrepancy in the recommended bulk charge rates. Does anyone on the forum have a recommendation on what approach to take based on your experience with AGM's??
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Old 04-06-2014, 02:06 PM   #2
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Sounds like you have visited the Lifeline web site a few times. I too have the Lifeline AGM's and set my charger for them. It is interesting that Magnum has a setting just for Lifeline AGM's .

Maybe a call to AM solar would help you. They are a dealer for Magnum and Lifeline.

When they installed my solar they were happy to see that i had Lifeline baterries. Set my solar charger controller for the Lifeline's and said if I change brands to call them to change the setting.

Was told that the charge rate would be lower for other brands.
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Old 04-06-2014, 05:28 PM   #3
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Quote:
Originally Posted by MN_Traveler View Post
While the inverter/charger's manual DOES state "the C/5 or C/20 charge rate settings are guidelines ... for specific charge rate requirements, refer to your battery manufacturer.". I was aware that AGM's are able to tolerate faster charge times, but this is a HUGE discrepancy in the recommended bulk charge rates. Does anyone on the forum have a recommendation on what approach to take based on your experience with AGM's??
This is one of my favorite Myths..

The C/5 (20 amps per 100 amps of capacity) is for LIFELINE only It used to be 30 by the way.

For most AGM's. that (30 percent) is the MAXIMUM bulk charge, same as for flooded wet cells and maintenance free.

OF all the batteries I have researched only LIFELINE recommends that as the minimum.

This does not mean there are not more that can do that.. Just that I have yet to come across them,, and I have looked.

The other myth.. AGM's last longer

My MK (East Penn battery CO) AGMs lasted 5 years
My Flooded Wet Cells (Interstate) 9
My Maintenance free,, not sure but 8-10 would be the range.

Yup, AGM's were last in, first out.
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Old 04-06-2014, 08:53 PM   #4
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Your Lifelines will be fine at a charge rate of C/5. If you have more charge capacity and input AC current capacity you can increase the charge rate, but don't have to.

You have more capacity than I've heard of. I have a single bank with 6 8D Lifelines, but the one bank supports 2 2500w inverters.
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Old 04-06-2014, 10:36 PM   #5
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You may absolutely charge your Lifelines with all the Amps you can find. Some people will daisy chain chargers to get more amps and cut down the charge time. Of course...at some point...you run out of "wall current!!
This is true for Lifelines and Odysseys and the sears diehard Platinum made by Odyssey.
Despite what the lawyers put on other AGM's .... most TRUE DEEP CYCLE AGMS will easily withstand charge rates of C/2.

Given that the Magnums come in either 100 or 125amp chargers...sounds like your main concern is using a rate that is under the recommendation. The C20 is a general guideline and you're close enough not to worry about it in my opinion with either the 125 or 100 amp chargers.
If you wanted to be super cautious...I'd divide in to two banks with a battery switcher like the Perkos...a 400 amp bank and a 200 amp bank. You could independently charge them that way and use the "both" position to get the most from Mr. Peukert. ....That would tend to be a pain though. Personally I wouldn't bother and I give you full permission to blame me when you get 490 cycles instead of 500!
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Old 04-08-2014, 08:30 PM   #6
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. Given that the Magnums come in either 100 or 125amp chargers...sounds like your main concern is using a rate that is under the recommendation. The C20 is a general guideline and you're close enough not to worry about it in my opinion with either the 125 or 100 amp chargers. If you wanted to be super cautious...I'd divide in to two banks with a battery switcher like the Perkos...a 400 amp bank and a 200 amp bank. You could independently charge them that way and use the "both" position to get the most from Mr. Peukert. ....That would tend to be a pain though. Personally I wouldn't bother and I give you full permission to blame me when you get 490 cycles instead of 500!
CORRECT, I was worried about charging at too low a rate (though the highest rate is, by the numbers, something like 3000 (sic) amps, I somehow doubt I would be able to supply that. :-). . I do have two charger/inverters on the bank though, so unless they do not interfere with each other, I should be ok on 100% rate settings on both of them.

Thank you all for the input !
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Old 04-08-2014, 08:42 PM   #7
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The other myth.. AGM's last longer My MK (East Penn battery CO) AGMs lasted 5 years My Flooded Wet Cells (Interstate) 9 My Maintenance free,, not sure but 8-10 would be the range. Yup, AGM's were last in, first out.
WA8YXM: thanks for relating your experience. In my case, I am not retired ... So maintenance time is my primary concern. I wish for the agm's mostly for their 1) lack of need to monitor fluid level, 2) lack of venting ( my previous batteries were quite "colorful" even though I tried to keep them clean and treated with inhibitor, and 3) their much reduced internal discharge rate (maintaining the state of charge of flooded cell batteries in the winter in Minnesota when it is 20 BELOW for days or weeks on end is ...challenging. Anything that reduces my time paying attention to the above three items is worth additional cost, at least for now. I am not intending to start another flooded cell versus AGM debate: I consider this a case of FWIW and IMHO.
Cheers.
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Old 04-08-2014, 10:24 PM   #8
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For what it may be worth, my first set of AGM's lasted 10 trouble free years of fulltiming. The current set is two years old and looking good.
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Old 04-09-2014, 10:47 AM   #9
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Again, you support my claim that the "Longer life" of AGM's is a myth.

My factory Flooded wet cells made it almost (next month) to 9 years (I replaced them last week) and I do not know how old they were when I took delivery, The Maintenance free chassis battery dates back to Auguest 2004 per Workhorse (When chassis was shipped) and it got replaced last Feburary.

That is close enough to 10 years for me. I might add I abused my Flooded wet cells some.
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Old 04-09-2014, 12:35 PM   #10
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My 8D Lifeline AGMs turned 10 years old in January. No problems with them. On the plus side, I don't have to water them and I haven't got holes in my clothes from spilled acid.
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Old 04-09-2014, 05:00 PM   #11
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Again, you support my claim that the "Longer life" of AGM's is a myth.

My factory Flooded wet cells made it almost (next month) to 9 years (I replaced them last week) and I do not know how old they were when I took delivery, The Maintenance free chassis battery dates back to Auguest 2004 per Workhorse (When chassis was shipped) and it got replaced last Feburary.

That is close enough to 10 years for me. I might add I abused my Flooded wet cells some.
Good for you!

I'll keep my AGM's!
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Old 04-09-2014, 08:09 PM   #12
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Wet cells can certainly take more abuse. For me, I'll stay with my AGMs. My house bank is in a vented box in a bay, but I don't want the hassle and maintenance of wet cells in this application.

AGM owners need to realize they can gas if significantly overcharged. Once this happens they are no longer sealed.

Ultimately, it's a personal choice unless the batteries are in the living area or unvented compartment.
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