What is the optimal SOC range for cycling AGM batteries

Coach Dad

Feeding off Vtmaps’ thread “what is the optimal SOC range for cycling lead acid batteries” I didn’t want to sidetrack his post but I would be curious if the same rules apply for AGM batteries.

Vtmaps wrote:

I have noticed that most (all?) battery manufacturers that provide life cycle information define a cycle as reaching 100% SOC. The data always shows that shallow cycling will result in more cycles than deep cycling. Thus more cycles from 80% to 100% than from 70% to 100% SOC.

This is agrees with the charts which are included in the Sun Xtender AGM battery manual.

I understand that AGM batteries do take a higher rate of charge and discharge than the flooded batteries do.
I understand that AGM batteries are more resistant to sulphation than flooded batteries..
But
I also understand that AGM batteries cannot be refilled and therefore should avoid Equalizations.
So my instinct tells me that limiting the SOC (or discharge) would also require less Absorbtion time for recharge which can increase the life of AGM batteries

Vtmaps also wrote:

I certainly understand that batteries accept charge more efficiently at lower SOC, but my personal preference is to sacrifice efficiency for longevity... a few extra panels (one time expense) will make up for the inefficiency.

I agree with this logic and would like the resident experts to weigh in when it comes to AGM’s.

NorthGuy

Re: What is the optimal SOC range for cycling AGM batteries

Coach Dad wrote: »

So my instinct tells me that limiting the SOC (or discharge) would also require less Absorbtion time for recharge which can increase the life of AGM batteries.

I think it's the oposite. Deeper discharges (cycling between 50 to 80% SoC) help avoid absorption because most of the charging is moved to bulk phase. This lets you do absorption only every 3 (7, 10?) cycles. If you cycle between 80 and 100% SoC, all your charging is absorption.

I don't know if that's true, but I would think that deeper cycling is even more advantageous for AGMs than for FLAs because there's no adverse effects of electrolyte staratification.

vtmaps

Re: What is the optimal SOC range for cycling AGM batteries

NorthGuy wrote: »

I would think that deeper cycling is even more advantageous for AGMs than for FLAs because there's no adverse effects of electrolyte stratification.

Quite the contrary. It was discussed and referenced here: http://forum.solar-electric.com/showthread.php?p=137202#post137202

And here is another reference:
Abstract of a paper about Gel and AGM batteries:

It is well known that GEL batteries have higher cycle life and operational life than AGM batteries. Further, AGM batteries are more sensitive to acid stratification and thermal runaway, but have a lower internal resistance. These characteristics depend on the different SiO2 structure in GEL and AGM. This paper discusses these issues. http://www.battcon.com/PapersFinal2007/RuschPaper2007.pdf

Excerpts from http://www.battcon.com/PapersFinal2007/RuschPaper2007.pdf

AGM batteries have a height restriction. Plates with a height above 200mm suffer from acid stratification, while GEL batteries can be built without practical restriction.
<snip>
Even for cells with plate heights of 100mm up to 200mm, acid stratification may occur, if thinner plates are used unintentionally or the container bulges out.

--vtMaps

zoneblue

Re: What is the optimal SOC range for cycling AGM batteries

Count me as interested in agms as well. Mine are very lightly cycled, and are tallish 2v cells (330mm case). Thing is its not a big bank 400 Ah at 24v, hence im protective, maybe overly so of their capacity. These cells have telecomunications UPS in their blood line im pretty sure, even though they are advertised as suitable for RE, i think that was an after thought. I know from experience that UPS batterys often have short lives.

The best i can think of is to reduce absorb voltage to 27v (present float), and do a weekly equalise at 28.2. These cells seem to have lowish recomended voltages anyway. And put them on their sides.

PNjunction

Re: What is the optimal SOC range for cycling AGM batteries

Cycling agm's from say 50-85% SOC is often encountered in marine environments where the captain does not want to burn diesel every day during absorb and having to cut his trip short. It might be interesting to look at the voluminous threads about this in the Sailnet community forums. Morgan's Cloud used to have material on it as well.

I know that Justin Godber of Lifeline (one of the few agm's that can be EQ'ed, but not recommended as daily thing) states that doing 50-85% daily and you may last a year. 50-85 with an occasional EQ might get you up to 4 years. 100% charge (completion of absorption) and an occasional EQ raises that figure to maybe 5 years. 100% charge daily is the longest. But then again, this is for Lifeline agm's which are different from most others. These yearly figures are from memory in reading about it on the Morgan's Cloud saga a few years ago, so I might be off a bit.

Aside from SOC, one thing that may be overlooked is the *minimum* current needed to prolong life with AGM's as well. Everything I've read from manufacturers points to not tickling agm's to death with insufficient current since they have much lower internal resistance for better charge acceptance, ie more charging and less heat.

For example, East Penn / Deka states in their VRLA application guide, the for longest life, one should strive to achieve the maximum inrush current of around .3C as long as it stays within the proper temperature and voltage. That's easy to miss in their guide since it is part of the "tips" paragraph.

I know that Lifeline recommends 0.2C minimum, and Odyssey/Enersys recommends 0.4C minimum. I'm thinking that this could be eased a *little* bit if you stay less than 50% DOD. If you don't do this and tickle your agm's, they state that you'll be "walking down" the capacity little by little each cycle.

Depending on the size your agm bank, I wonder just how many solar systems running agm's are not even reaching 0.1C ?

As a side note, with only a voltmeter to guide us in static SOC measurements, I found a cheap meter which will measure the internal resistance:

Cen-Tech "Digital Automotive Battery Tester". Ok, go ahead and laugh. Although I'm not interested in CCA readings whatsoever, it was the only one that was affordable to the common-man which actually measures internal impedance. I'm going to use that as a relative reference to help keep an eye on my agm's. It feels like a cheap toy, but maybe that internal impedance measurement will come in handy as my batteries age and let me know beforehand if I'm hurting them with bad charge procedures.

tons001

Re: What is the optimal SOC range for cycling AGM batteries

PNjunction wrote: »

Cen-Tech "Digital Automotive Battery Tester". Ok, go ahead and laugh. Although I'm not interested in CCA readings whatsoever, it was the only one that was affordable to the common-man which actually measures internal impedance. I'm going to use that as a relative reference to help keep an eye on my agm's. It feels like a cheap toy, but maybe that internal impedance measurement will come in handy as my batteries age and let me know beforehand if I'm hurting them with bad charge procedures.

Will the meter do anything above a 12v battery? My bank is 24v.

Coach Dad

Re: What is the optimal SOC range for cycling AGM batteries

PNjunction wrote: »

Cycling agm's from say 50-85% SOC is often encountered in marine environments where the captain does not want to burn diesel every day during absorb and having to cut his trip short. It might be interesting to look at the voluminous threads about this in the Sailnet community forums. Morgan's Cloud used to have material on it as well.

I know that Justin Godber of Lifeline (one of the few agm's that can be EQ'ed, but not recommended as daily thing) states that doing 50-85% daily and you may last a year. 50-85 with an occasional EQ might get you up to 4 years. 100% charge (completion of absorption) and an occasional EQ raises that figure to maybe 5 years. 100% charge daily is the longest. But then again, this is for Lifeline agm's which are different from most others. These yearly figures are from memory in reading about it on the Morgan's Cloud saga a few years ago, so I might be off a bit.

Aside from SOC, one thing that may be overlooked is the *minimum* current needed to prolong life with AGM's as well. Everything I've read from manufacturers points to not tickling agm's to death with insufficient current since they have much lower internal resistance for better charge acceptance, ie more charging and less heat.

For example, East Penn / Deka states in their VRLA application guide, the for longest life, one should strive to achieve the maximum inrush current of around .3C as long as it stays within the proper temperature and voltage. That's easy to miss in their guide since it is part of the "tips" paragraph.

I know that Lifeline recommends 0.2C minimum, and Odyssey/Enersys recommends 0.4C minimum. I'm thinking that this could be eased a *little* bit if you stay less than 50% DOD. If you don't do this and tickle your agm's, they state that you'll be "walking down" the capacity little by little each cycle.
Depending on the size your agm bank, I wonder just how many solar systems running agm's are not even reaching 0.1C ?

PNJ.. That is good insight. I have Sun-Xtender batteries. These batteries are supposedly designed for use in Solar Electric (PV) Systems so I wonder if the same rules apply… But since Concorde battery owns both Lifeline and Sun-Xtender, I also wonder if the same rules apply to both AGM types. I think Lifelines are intended for marine/RV use while Sun-Xtender are PV specific.
But for all I know,,, they could be the same batteries with different labels.

The Sun-Xtender manual recommends that you use as high an inrush of charge current as possible up to 5C and recommend 0.2C for repetitive “deep cycling”.

The manual also states that the “average” daily discharge should be limited to 20% (80% SOC)… Here is the Manual recommendation.
Attachment not found.
The reason I started this thread was that the experts here are advocating much deeper discharges on flooded batteries which contradicts the Sun-Xtender AGM manual. All of this is confusing me to no end.

Blackcherry04

Re: What is the optimal SOC range for cycling AGM batteries

Coach Dad wrote: »

PNJ.. That is good insight. I have Sun-Xtender batteries. These batteries are supposedly designed for use in Solar Electric (PV) Systems so I wonder if the same rules apply… But since Concorde battery owns both Lifeline and Sun-Xtender, I also wonder if the same rules apply to both AGM types. I think Lifelines are intended for marine/RV use while Sun-Xtender are PV specific.
But for all I know,,, they could be the same batteries with different labels.

The Sun-Xtender manual recommends that you use as high an inrush of charge current as possible up to 5C and recommend 0.2C for repetitive “deep cycling”.

The manual also states that the “average” daily discharge should be limited to 20% (80% SOC)… Here is the Manual recommendation.

The reason I started this thread was that the experts here are advocating much deeper discharges on flooded batteries which contradicts the Sun-Xtender AGM manual. All of this is confusing me to no end.

Another manual writer that can't do math or write a plain explanation, 5 day's @ 10% would give you the Autonomy they recommend or 50 % DOD.

They are in the business to sell Batteries, lot's of Batteries, I guess they never heard of a generator and charger.

Cariboocoot

Re: What is the optimal SOC range for cycling AGM batteries

"6.2 days of autonomy". Wow. There's some horrible out-of-date advice.

Coach Dad

Re: What is the optimal SOC range for cycling AGM batteries

Cariboocoot wrote: »

"6.2 days of autonomy". Wow. There's some horrible out-of-date advice.

6.2 is the manual section number....
They are recommending 5 days of autonomy..

niel

Re: What is the optimal SOC range for cycling AGM batteries

blackcherry is right as 20% per day for 5 days will be 0% soc. by our standards the autonomy is really 2.5 days as we try to extend the life cycle of a battery rather than kill it. to us it would be 5 days in an emergency or extenuating circumstances only.

i do remember a life cycle graph long ago that showed the peak for sunxtenders at just under 70% soc as optimum all things considered.

Coach Dad

Re: What is the optimal SOC range for cycling AGM batteries

i do remember a life cycle graph long ago that showed the peak for sunxtenders at just under 70% soc as optimum all things considered.

Is this the graph?
Attachment not found.

zoneblue

Re: What is the optimal SOC range for cycling AGM batteries

You might remember that my life cycle curve here:

http://forum.solar-electric.com/showthread.php?18049-Depth-of-discharge&p=137789#post137789

Its shows a theoretical case for deeper discharges. However i have done this Wh per liftime curve for some FLA banks and the result is usually much much flatter. ie DOD agnostic.

Heres the same analysis for the concorde lifecycle curve below. Quite a different curve, but one closely resembling the conventional wisdom.

Attachment not found.

Of course the definition of a cycle is always a bit vague.

Blackcherry04

Re: What is the optimal SOC range for cycling AGM batteries

There is also another chart that they never publish, it's the one that would show that you can take the battery and put it on a float charger and never cycle it and 5 years it'll be worthless.

mtdoc

Re: What is the optimal SOC range for cycling AGM batteries

Blackcherry04 wrote: »

There is also another chart that they never publish, it's the one that would show that you can take the battery and put it on a float charger and never cycle it and 5 years it'll be worthless.

I don't know about SunXtenders but for Odyssey AGM's float life is specified at 10+ years. From their Technical Manual

Since ODYSSEY® batteries are dual purpose by design, they
offer a long-life battery option in float applications. At room
temperature (77°F or 25°C) these batteries have a design life of
10+ years in float applications; at end of life an ODYSSEY battery
will still deliver 80% of its rated capacity.

Blackcherry04

Re: What is the optimal SOC range for cycling AGM batteries

mtdoc wrote: »

I don't know about SunXtenders but for Odyssey AGM's float life is specified at 10+ years. From their Technical Manual

Dry cell acid Battery, total different animal.

lol..... Real Proud of it , aren't they.

EnerSys Energy Products Inc. (“Manufacturer”) warrants its ODYSSEY® batteries (hereafter referred to as “Battery”) to be free of defects in material and workmanship for the following Applicable Warranty Periods:

2 years for Auxiliary Power Unit (APU) and other non engine start cycling applications
2 years for power sports applications
3 years for commercial, industrial, marine and automotive applications in non BCI sizes.
4 years for an engine starting application for PC1220, PC1350, PC2250 and all BCI sizes.

zoneblue

Re: What is the optimal SOC range for cycling AGM batteries

Blackcherry04 wrote: »

There is also another chart that they never publish, it's the one that would show that you can take the battery and put it on a float charger and never cycle it and 5 years it'll be worthless.

Im fine with exuburant statements, we should all make a few from time to time However it would be more useful to the conversation if you were willing to justify or reference them.

I guess im also interested, given the variance in life cycle charts between manufacturers, in the source of the manufacturers life cycle data. Its not likely to be easy to obtain. Sure you could set up an automated charge discharge machine, but that would necessaryly differ from the timescale of real life applications.

Blackcherry04

Re: What is the optimal SOC range for cycling AGM batteries

zoneblue wrote: »

Im fine with exuburant statements, we should all make a few from time to time However it would be more useful to the conversation if you were willing to justify or reference them.

I guess im also interested, given the variance in life cycle charts between manufacturers, in the source of the manufacturers life cycle data. Its not likely to be easy to obtain. Sure you could set up an automated charge discharge machine, but that would necessaryly differ from the timescale of real life applications.

Take a hint from the Telecom companies, how long do they keep a set of Batteries that are lightly cycled ?? Probably only cycled when tested, 5 Years. Thats my part of the conversation. Someone must be really naive to believe that a battery will ever last long enough years to do 5,000 cycles.

mtdoc

Re: What is the optimal SOC range for cycling AGM batteries

Blackcherry04 wrote: »

Dry cell acid Battery, total different animal.

Nope, they're AGMs.

Blackcherry04

Re: What is the optimal SOC range for cycling AGM batteries

mtdoc wrote: »

Nope, they're AGMs.

Yep, Dry cell acid. All you have to do is read their literature. You can call it anything you want. How about that warranty, you can float it 10 years, but the max warranty is 4 years, 3 on the deep cycle. They know the catalysts won't last 10 years and once they go there is no recombining and they turn to tar inside.

zoneblue

Re: What is the optimal SOC range for cycling AGM batteries

But whos to say that they arent just being cautious. When i was in the miltary we decomissioned nicads when they dropped below exactly 100% load tested nominal capacity. We took them home and used them in our cars for years afterwards.

The other brand of readily available 2v agms cells available here claims a service life of 15 years in float applications.

"In float applications (such as stand-by power supplies)... the GM series batteries 10 to 15 years. In typical* Remote Area Power Supply, Motorhome, and Deep-Cycle Marine applications, the expected service life of the ... GM 2 volt series is 15 to 20 years."
- http://aasolar.co.nz/AA%20Champion%20AGM%20Deep%20Cycle%20Batteries.html

So are we any further forward?

niel

Re: What is the optimal SOC range for cycling AGM batteries

i'm not sure why all of this talk of years of float charging. isn't a battery that is always on float and never used somewhat worthless?

Blackcherry04

Re: What is the optimal SOC range for cycling AGM batteries

zoneblue wrote: »

But whos to say that they arent just being cautious. When i was in the miltary we decomissioned nicads when they dropped below exactly 100% load tested nominal capacity. We took them home and used them in our cars for years afterwards.

The other brand of readily available 2v agms cells available here claims a service life of 15 years in float applications.

"In float applications (such as stand-by power supplies)... the GM series batteries 10 to 15 years. In typical* Remote Area Power Supply, Motorhome, and Deep-Cycle Marine applications, the expected service life of the ... GM 2 volt series is 15 to 20 years."
- http://aasolar.co.nz/AA%20Champion%20AGM%20Deep%20Cycle%20Batteries.html

So are we any further forward?

Yeah, were a lot further ahead. Since you posted it. One year full warranty.

5. Warranty for 6 and 12 VDC batteries is 5 years pro rata on 60 months. First year, full replacement if battery fails under warranty condition and pro rata for a further 4 years based on 60 months and the recommended retail price at the time of warranty claim including GST

6. Warranty for 2 VDC cells is 6 years pro rata on 72 months. First 1 year full replacement if batteries fail under warranty conditions, and a further 5 years based on 72 months and the recommended trade price at the time of warranty claim including GST

http://aasolar.co.nz/AA%20Champion%20AGM%20Deep%20Cycle%20Batteries.html

Blackcherry04

Re: What is the optimal SOC range for cycling AGM batteries

niel wrote: »

i'm not sure why all of this talk of years of float charging. isn't a battery that is always on float and never used somewhat worthless?

Thats the point, if their chart shows that you'll get 5,000 cycles at 10% dod, it'll never last long enough to complete those cycles and their warranty shows it won't and they know it.

mtdoc

Re: What is the optimal SOC range for cycling AGM batteries

Blackcherry04 wrote: »

Yep, Dry cell acid. All you have to do is read their literature. You can call it anything you want.

I'm quite familiar with their literature. Here is the first sentence from their technical manual:

The ODYSSEY® battery ingeniously uses absorbed glass mat (AGM) valve regulated lead acid (VRLA) technology to offer, in
one package, the characteristics of two separate batteries. It can deep cycle as well as deliver serious cranking power ..

They do use what they call "pure lead technology- but they are AGMs. Period.

How about that warranty, you can float it 10 years, but the max warranty is 4 years, 3 on the deep cycle. They know the catalysts won't last 10 years and once they go there is no recombining and they turn to tar inside.

Not sure what their warranty has to do with it - it has nothing to do with float life.

If there is some super, double top secret document that says some AGM battery will only last 5 yrs when floated - please reference it. It certainly might be true for some AGMs - but not for Odysseys.

I'm sure there are shady companies out there but Enersys (maker of Odyssey) - has a very good reputation and would be foolish to publish in their technical manual a float life of 10+ years for their AGM batteries if it was not true.

BTW- Neil - the importance of float life - is for batteries used in a "back up" application. Hopefully never used - but if so you wan't to know their lifespan.

Blackcherry04

Re: What is the optimal SOC range for cycling AGM batteries

mtdoc wrote: »

I'm quite familiar with their literature. Here is the first sentence from their technical manual:



They do use what they call "pure lead technology- but they are AGMs. Period.





Not sure what their warranty has to do with it - it has nothing to do with float life.

If there is some super, double top secret document that says some AGM battery will only last 5 yrs when floated - please reference it. It certainly might be true for some AGMs - but not for Odysseys.

I'm sure there are shady companies out there but Enersys (maker of Odyssey) - has a very good reputation and would be foolish to publish in their technical manual a float life of 10+ years for their AGM batteries if it was not true.

BTW- Neil - the importance of float life - is for batteries used in a "back up" application. Hopefully never used - but if so you wan't to know their lifespan.

Here I'll split the difference with you. Still a different technology. I have 2 of them in a couple Jet Skis, I don't have a issue yet. Easy to see who they are after Optima.


http://www.odysseybattery.com/batteries.html

Like many popular spiral-wound batteries, ODYSSEY batteries employ dry cell AGM technology to contain acid, allowing the battery to be installed even on its side. But the densely packed flat plates in an ODYSSEY battery avoid the “dead space” between cylinders in a “six-pack” design. The result is 15% more plate surface area — and that translates to more power!

zoneblue

Re: What is the optimal SOC range for cycling AGM batteries

The GM series (somwhat similar to my bank at least in size, weight etc), so 6 year warranty.

As for our host... he says:
" For example, one of the widely advertised telephone type (float service) batteries have been advertised as having a 20-year life. If you look at the fine print, it has that rating only at 5% DOD - it is much less when used in an application where they are cycled deeper on a regular basis."
- http://www.solar-electric.com/deep-cycle-battery-faq.html#Cycles%20vs%20Life

Im not trying to be argumentive, and i certainly dont know whats right or wrong, and whether it makes a difference which brand, or how the plates are built, or whatever but the fact that agms are a nontransparent black box, i think if we are going to shed any light on the subject, it best come with data.

mtdoc

Re: What is the optimal SOC range for cycling AGM batteries

Blackcherry04 wrote: »

Here I'll split the difference with you. Still a different technology. I have 2 of them in a couple Jet Skis, I don't have a issue yet. Easy to see who they are after Optima.


http://www.odysseybattery.com/batteries.html

Like many popular spiral-wound batteries, ODYSSEY batteries employ dry cell AGM technology to contain acid, allowing the battery to be installed even on its side. But the densely packed flat plates in an ODYSSEY battery avoid the “dead space” between cylinders in a “six-pack” design. The result is 15% more plate surface area — and that translates to more power!

I think they use the term "dry cell" to distinguish them from flooded batteries. Since the places in their marketing literature where they use that term it is in contrast to flooded batteries for example in your quote - saying they can be installed on their side (as could any AGM). I think it is just marketing speak and has nothing to do with any fundamental difference in technology. I've never seen any reference to it in their technical documents.

In general AGMs are known to have a longer float life than FLAs since they don't suffer from the same stratification issues. This is why they are more typcially used in back up applications. The tradeoff is they typically do not repeatedly deep cycle as well...

I have 8 of their pc 1800s. They are floated >95% of the time - only being taken down when we have a power outage or when I occaionally cycle them to test my system. I've only had them 3 yrs so far but they've shown no loss of capacity yet. I know of someone who has used them in a marine cruising application for > 5 yrs with no signs of any loss of capacity yet. Most of the time his are floated as well.

Blackcherry04

Re: What is the optimal SOC range for cycling AGM batteries

mtdoc wrote: »

I think they use the term "dry cell" to distinguish them from flooded batteries. Since the places in their marketing literature where they use that term it is in contrast to flooded batteries for example in your quote - saying they can be installed on their side (as could any AGM). I think it is just marketing speak and has nothing to do with any fundamental difference in technology. I've never seen any reference to it in their technical documents.

In general AGMs are known to have a longer float life than FLAs since they don't suffer from the same stratification issues. This is why they are more typcially used in back up applications. The tradeoff is they typically do not repeatedly deep cycle as well...

I have 8 of their pc 1800s. They are floated >95% of the time - only being taken down when we have a power outage or when I occaionally cycle them to test my system. I've only had them 3 yrs so far but they've shown no loss of capacity yet. I know of someone who has used them in a marine cruising application for > 5 yrs with no signs of any loss of capacity yet. Most of the time his are floated as well.

I'll take my crow with some A1 sauce on it, please. I think you are more right than I was. I just always heard there was something different about them. I have had a bad year with AGM's, I am sure they have a place, but I'v had 3-4 fail and they were all high dollar batteries with no long term warranty. I am starting to read that fine print more and separate out the marketing hype.

mtdoc

Re: What is the optimal SOC range for cycling AGM batteries

Blackcherry04 wrote: »

I'll take my crow with some A1 sauce on it, please..

Well - we'll see -If my Odysseys go belly up in the next couple of years I'll join you in the crow eating fest...:p

It sure would be nice if there was a deep cycle AGM or SLA for that matter) out there that had a 10 yr warranty......

Batteries remain the weak link in RE systems IMHO.

vtmaps

Re: What is the optimal SOC range for cycling AGM batteries

mtdoc wrote: »

In general AGMs are known to have a longer float life than FLAs since they don't suffer from the same stratification issues.

mtdoc, AGMs do suffer from stratification issues. Please look at the third post in this thread, and if you click on the first link you will see one of your previous postings in which you knew that AGMs have stratification issues.

--vtMaps