BU-201a: Absorbent Glass Mat (AGM)

AGM technology became popular in the early 1980s as a sealed lead acid battery for military aircraft, vehicles and UPS to reduce weight and improve reliability. The acid is absorbed by a very fine fiberglass mat, making the battery spill-proof. This enables shipment without hazardous material restrictions. The plates can be made flat to resemble a standard flooded lead acid pack in a rectangular case; they can also be wound into a cylindrical cell.

AGM has very low internal resistance, is capable to deliver high currents on demand and offers a relatively long service life, even when deep-cycled. AGM is maintenance free, provides good electrical reliability and is lighter than the flooded lead acid type. It stands up well to low temperatures and has a low self-discharge. The leading advantages are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life.  The negatives are slightly lower specific energy and higher manufacturing costs that the flooded. AGM has a sweet spot in midsize packs from 30 to 100Ah and is less suitable for large UPS system.  

AGM batteries are commonly built to size and are found in high-end vehicles to run power-hungry accessories such as heated seats, steering wheels, mirrors and windshields. NASCAR and other auto racing leagues choose AGM products because they are vibration resistant. AGM is the preferred battery for upscale motorcycles. Being sealed, AGM reduces acid spilling in an accident, lowers the weight for the same performance and allows installation at odd angles. Because of good performance at cold temperatures, AGM batteries are also used for marine, motor home and robotic applications.

Ever since Cadillac introduced the electric starter motor in 1912, lead acid became the natural choice to crank the engine. The classic flooded type is, however, not robust enough for the start-stop function and most batteries in a micro-hybrid car are AGM. Repeated cycling of a regular flooded type causes a sharp capacity fade after two years of use. See Heat, Loading and Battery Life.

As with all gelled and sealed units, AGM batteries are sensitive to overcharging. These batteries can be charged to 2.40V/cell (and higher) without problem; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell), and a direct replacement with a sealed unit could spell trouble by exposing the battery to undue overcharge on a long drive. See Charging Lead Acid.

AGM and other sealed batteries do not like heat and should be installed away from the engine compartment. Manufacturers recommend halting charge if the battery core reaches 49°C (120°F). While regular lead acid batteries need a topping charge every six months to prevent the buildup of sulfation, AGM batteries are less prone to this and can sit in storage for longer before a charge becomes necessary. Table 1 spells out the advantages and limitations of AGM.
 

Advantages

Spill-proof through acid encapsulation in matting technology

High specific power, low internal resistance, responsive to load

Up to 5 times faster charge than with flooded technology

Better cycle life than with flooded systems

Water retention (oxygen and hydrogen combine to produce water)

Vibration resistance due to sandwich construction

Stands up well to cold temperature

Limitations

Higher manufacturing cost than flooded (but cheaper than gel)

Sensitive to overcharging (gel has tighter tolerances than AGM)

Capacity has gradual decline (gel has a performance dome)

Low specific energy

Must be stored in charged condition (less critical than flooded)

Not environmentally friendly (has less electrolyte, lead that flooded)

Table 4: Advantages and limitations AGM. The gel system shares many of the characteristics.

Comments

On May 27, 2012 at 9:42pm
Jean L Genibrel wrote:

Speaking from experience with flooded, gel and AGM batteries I can safely say that AGM batteries do not have better cycle life than flooded and certainly not that of gel. The only advantage to AGM batteries is that the seller can claim high Cold Cranking Amperage, which in the real world is pretty much meaningless but those big numbers appeal to the buying public. Keep in mid that in order to create an AGM battery the plates must be very thin in comparison to a flooded battery or a gel one. This type of construction allows for higher CCAs but lower cycling ability. real cycling should be undertaken to 10v not just 12.6 or12.7.

On September 16, 2012 at 11:13pm
jon sansfras wrote:

AGM can come in starting and deep cycle like any other battery. They’re not inherently more capable of deep discharge. I’m finding alot of just plain wrong info on this site.

On November 3, 2012 at 12:14pm
Chris Swol wrote:

I’ve been selling marine batteries for 11 years now at WM.  I’m just now seeing AGM’s coming in for replacement.  Operator error is prevelant with flooded, gel and AGM.  Any battery properly maintained and a good charging systen wiil give a battery a long life.  My Dodge and Sears batteries are still going strong after 42 months in the hot weather in Florida.  Clean your terminal at least twice a year!!
Chris

On December 12, 2012 at 3:59pm
Paul Dumstorf Sr. wrote:

Ref jon sansfras’ comments on inaccuracies in these battery University publications, my question to him?. What is the name of the publications you author, I’m sure everyone would much rather read what you have written than this inaccurate information, why do you waste your time reading this stuff any way if your so damn smart?

On February 18, 2013 at 3:12am
kieran zero wrote:

Fred - particularly sad to be trolling a battery university site.
I’ve heard of energy vampires, but . . . . . lol . . .

And to the author of this site; thanks for this rather excellent resource!

On June 4, 2013 at 6:42am
battery yes wrote:

AGM was not developed in 1985, it was developed earlier than that.  In 1985 there were several battery companies already manufacturing AGM batteries by then

On June 19, 2013 at 8:04am
The Great Equalizer wrote:

battery yes - I am having trouble with your comment. are you saying that author is wrong or just rewording and supplementing the part where the author states “AGM technology became popular in the early 1980s?”

my two cents, I highly doubt the military would take an interest in a very expensive battery if it had lower performance expectancies than the competition.
If anyone would like to hear opinions and impressions of long time AGM battery owners miata.net would be a good place to start and, as Chris Swol was noticing, a lot of the Miata based AGM owners are reporting 10+ year lifespans with proper maintenance and care.

On June 19, 2013 at 8:10am
battery yes wrote:

the author initially stated that AGM was developed in 1985, which is simply untrue.  In 1985 there were several battery manufacturers in the US alone manufacturing AGM batteries.  The author reworded it to “became popular in the early 1908’s” which would make it accurate.

On September 24, 2013 at 3:40pm
Todd McNaughton wrote:

Well I do have to say that some readers comprehension is not very good. He stated that the AGM battery became “popular” in the 80’s, And to the other reader, Yes the military does use AGM batteries for their tanks Hummers and all other pieces of equipment they have. Do some research before coming on here and bashing the author.

On September 24, 2013 at 3:49pm
Battery yes wrote:

Todd, read the whole string.  After I told him the dates if AGM usage, the author “reworded” the article. 
Read the entire string of comments before bashing us.  Maybe your reading comprehension needs to be improved.

On September 25, 2013 at 7:19am
Todd McNaughton wrote:

My comprehension is just fine I read it the way it is now, But thank you for your insightful comments, Its always a pleasure reading from such a knowledgeable expert.

On October 10, 2013 at 2:19am
jagdish wrote:

I want to know the material used to make AGM.

Content of AGM????

On October 16, 2013 at 3:02pm
Craig wrote:

All of the above is a lot of interpretation rather than factual however some have written good factual data.  But one very important difference between the AGW and Deep Cycle is the AGW is not meant for storage but rather continuous use, whereas the deep cycle can take storage very well going and letting the potential run well below the critical mark of 50% charge of the AGW.

On October 20, 2013 at 3:07pm
CJ wrote:

Question. My 200 Ah AGM is installed on a boat that sits idle for up to a month or more at a time and then gets a lot of use for a while then sits idle again. When I was having trouble with the last battery I installed a new one and was told “better to keep it on charge all the time when not in use”. Did that but after three years the battery takes but will not retain a charge. Any advice for care of the inevitable new one?

On November 5, 2013 at 12:00pm
BiShaL wrote:

i have a 2013 audi a8l hybrid and it got two 12v agm battery,one 75ah another 36ah in the funk..also it is equipped with a high voltage battery..i wanna charge the 12v 75ah battery as i don’t drive the car very often..
so should i use a battery charger if yes which one(i guess ctek mxs 5.0)..
as there is other battery involve will the charging be harmful??
please advise..thanks in advance..

On November 9, 2013 at 12:54am
Whynot wrote:

AGM battery’s made in China are Junk! I can’t say about the one made in other places, Didn’t make it to the 2nd year. My stock battery lasted 6 years.

On January 5, 2014 at 12:08pm
VAGELIS wrote:

Hello!
I want to buy for my bike Battery AGM , i want to ask if it will be better than another!!

thanks!!

On January 8, 2014 at 11:01am
VAGELIS wrote:

Hello!
I want to buy AGM battery,for my motorcycle, I want to ask if it is better than the yuasa??

Thanks!

On January 20, 2014 at 10:18am
Andrew wrote:

Two Lifeline 210Ah AGM batteries on my sailboat gave 9 years service before replacement. My wife and I cruise 6 months a year so they get heavy use. But I believe it’s meaningless to talk battery life without reference to the environment they live in—meaning the quality of the charging support plus the way they are used. Treat any battery well and you get a lot out of it. Treat an AGM well and you can grow old together.

On January 26, 2014 at 11:31am
Pete wrote:

I am using 4 U1 - SLA / AGM batteries for my electric scooter & they won’t last more than 1-1/2 years or so. . I started adding water to them after prying off the tops. . IS there another fluid I should be using ? ?  Pete . .  God Bless . . .

On January 27, 2014 at 12:31am
Bill wrote:

A very useful site. Unfortunate that there is no moderation to prevent rude or aggressive comments. My interest in batteries is for sailing yachts. The big advantage of AGM batteries in this application is their ability to accept higher charge rates than SLA batteries. Most voyaging yachts have to use their engines at least occasionally to recharge, which is bad for the engine and the environment. AGM batteries can reduce this time by up to 80%.

On March 26, 2014 at 12:09pm
Mike C wrote:

Anybody….. Which would be better….an AGM or a flooded deep cycle battery when used along with a power inverter as a back-up power supply into which you can plug a basement sump pump when there is a power outage?

On March 29, 2014 at 10:45am
Ferdous Azam Khan wrote:

While we compare AGM vs Flooded or Gell Batteries, then how could we write that “Not environmentally friendly (has less electrolyte, lead that flooded)” ! It should be ” environmentally friendly” as because less material being used, like no gell, no spillables etc. Am I reading it wrong?

On April 3, 2014 at 3:44pm
Matt S wrote:

Ladies and gentlemen good evening

Please does anyone know if I have to buy a “special” charger with 14.7v (and not 14.4v) to charge an AGM battery?

Cheers

On April 7, 2014 at 6:01pm
Lewis K wrote:

I am using AGM batteries for solar power storage.  Is it better to store the batteries at 65F inside, or at 30F to 50F in my house crawl space?  This article talks about high temperatures, but I am wondering if they are more efficient in cold temperatures between 30F and 50F verses a constant 65F.
Thank you.

On April 24, 2014 at 4:11pm
Lee Anderson wrote:

What do you think of the new Lead Crystal battery technology. I hear they are taking the market share in Africa and also started in Europe.

See Link:
http://leadcrystalbatteries.com/lead-crystal-batteries-technology/lead-crystal-batteries-performance/

I have ordered some batteries for testing.

Can any body elaborate on this?


Appreciate you feedback.

On April 28, 2014 at 3:38pm
TImothy Francis (Hypertechbatteries.com) wrote:

Now I may have missed this but I think the main advantage to having a AGM battery is because you can mount that sucker in any position, take it off-road, jump your truck a bunch of times and still have a battery that works.  I agree on the deep cycle properties of a AGM battery and in high drain applications will not work as well as a wet lead acid. With that said if your deep sea fishing and are encountering high seas and the bow of the boat is slamming the deck. Well those wet lead acids are going to fall apart and get acid everywhere.  AGM will stay together. So what it really breaks down to is durability vs cycle usage.  Lets just set the record straight gel is what it says gel. It’s the molasses of electrolyte. Lots of resistance. Also if the casing breaks it will still leak, slow.

On May 25, 2014 at 9:03pm
Ross Cherwinsk wrote:

Can anyone tell me if I could mount one of these batteries on its side. I know they say they are sp;ill proof but are they leak proof?

On May 26, 2014 at 6:22am
Alan wrote:

If your considering Motorcycle,  Lithium ion is even better.
Google LFX36L3-BS12

On June 11, 2014 at 11:38am
Mike Motorbike wrote:

Great info on this site, thank you.

re: Alan, lithium ion for motorcycle.

I researched this for my ‘82 450a Honda, and came to the conclusion an AGM was better. I got a med size $160 Deka AGM for from my local auto parts shop in BC Canada,  and shoe-horned it in.

Lithiums are still somewhat experimental for bikes, not mature technology yet.

Pro:
-LIthium has a supreme advantage for sport bikes with weight saving
- Huge discharge rate for spark and starter,
-They charge super fast, so less sitting discharged between rides, so when making many short rides they should recharge well.
-Hold that charge much better, so it is not necessary to plug-in after every ride. 

Con:
-They are not all waterproof, so put silicone on the lid of your Shorai.
-Tthere is a big controversy about the way Shorai (and some others) measure capacity. Pay more, get more. (but how much do you really need, as battery is used for short burst, only to start a bike)
-The bike’s charging system may be too high for lithium, get your voltage regulator specs.
-Buy the special optional lithium charger, and use only that (bring when traveling?)
-They are electronic devices with a lot of exposed wiring in the battery case, and there may be a protection circuit (which can drain the battery) so this can be a problem with current to much for wires, environmental corrosion (rust), and vibration affecting electronics.
-They don’t start in cold (hello fall and spring), so have to be warmed up (turn light on for a few min)
-Do lithiums last as long as AGM?
-Agms can be built rugged

Thank you guys for your contributions.

On June 21, 2014 at 6:50am
Louis wrote:

@Jean L Genibrel

You don’t need high cold cranking amperage in daily use??? I need it every day in my scooter 4T. It costs alot of amperage to start the ‘heavy’ 4T engine. I had a conventional Varta 9A battery wich wont have enough capacity anymore to start the engine after 1,5 year of daily use. I hope the AGM 9A will last longer, we’ll see.
Fortunately I am still able to use the Varta in my older 2T scooter, which needs alot less amperage for starting the engine

On August 6, 2014 at 7:14pm
Dave Fraser wrote:

I have a BMW R1200GS WC with a AGM 12v battery, BMW says I should not use a ACID/GEL trickle charger connected direct to AGM as it may damage CAM/Bus wiring and the battery.
Are they only trying to sell me a BMW charger ?

On August 10, 2014 at 11:01pm
Lithium smithium wrote:

Nice post Mike Motorbike
- you could also add to the “cons” list for lithium that they are not recyclable and have some unresolved safety issues.

> lead-acids are manufactured in a closed loop
> but basically every lithium battery uses newly mined lithium.. shocking waste and it’s yet another gold rush that will last as long until they have destroyed the world’s salt plains. But the lithium industry can’t make the price work if they do anything but dump used cells in landfill or occasionally pulp them for concrete production.

And you could also add safety…

Batteries in the lithium family have the distinct disadvantage of bursting into flame and releasing toxic fumes at inappropriate moments.

Lead-acids are non flammable and, as I understand AGM cells, they have very little electrolyte and you would be lucky to coax much acid out even if you drilled holes in it. (puncture a lithium battery at your peril).

On October 12, 2014 at 2:29pm
Nick wrote:

Be aware of what you’re using to charge and maintain AGM batteries.  Understand the purpose and specifications of whatever you use.

On October 14, 2014 at 8:13am
Mike Rogers wrote:

Can anyone explain to me the “sleep state ” a inactive AGM goes into and why?