BU-201a: Absorbent Glass Mat (AGM)

Learn what differentiate AGM from other lead acid battery types

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 sulfuric 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. While regular lead acid batteries need a topping charge every six months to prevent the buildup of sulfation, AGM batteries are less prone to sulfation and can sit in storage for longer before a charge becomes necessary. The battery stands up well to low temperatures and has a low self-discharge.

The leading advantages of AGM 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 than the flooded. 

Most AGM batteries are mid-sized and range from 30 to 100Ah. They 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.

AGM is making inroads into the start-stop function of cars. The classic flooded type is simply not robust enough and repeated cycling causes a sharp capacity fade after only two years of use. (See BU-806a: Heat, Loading and Battery Life.)

As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (and higher) is fine; 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); a direct replacement with a sealed unit could overcharge the battery on a long drive. (See BU-403: 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). Table 1 spells out the advantages and limitations of AGM.


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

Less prone to sulfation if not regularly topping charged


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 1: Advantages and limitations of AGM

Last updated 2016-04-15

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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!!

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:

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


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

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


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?


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:

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.

-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. 

-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?

On October 21, 2014 at 12:48pm
Ernesto Hafner wrote:

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.
My car is BMW X3 3000 and my battery Absorbent Glass Mat 12V 95Amps and as I use it not to often when I bought the battery they sold me a CLASS 2 BATTERY CHARGER MODEL LC-2152. I have used it and no problem as far as I know. Any comments please.???

On October 23, 2014 at 6:44am
John Douglas wrote:

https://www.youtube.com/watch?v=LOq6gy6bwRY   MUST WATCH for AGM batteries.

an AGM battery at 25c will last ~4 years, at 35c it will last 2 at ~20% DOD (depth of discharge)  in Australia, in Brisbane, we reach 40c in summer.  UGH!  why didn’t i know this before I bought 4 damn batteries!  *sigh*
know your environment temp range before looking at AGM.

On December 2, 2014 at 1:28am
CJ Miller wrote:

Don’t use a lithium battery in a Harley, unless you like to sit beside the road waiting for help!

On December 13, 2014 at 4:18am
Nils-Ove Halvorsen wrote:

The best AGM batteries I’ve come around, got years of experienced with many kind of starter & deep cycle battery in yacht and other sorts of sea crafts, There are one brand that stand out, in both design and lifetime, and it delivers more en expected.
Brand is: Ritar AGM Batteries.

But every battery must be cared for just like a pet !, I use to say regarding yachts that the batteries is the heart of the boat. wires as blood-vains, switches and relay as knee joints and so on…

On December 14, 2014 at 11:29am
L. M. North wrote:

Why have I been able to let my automobile batteries (gas-powered cars) sit outside in northeastern winters and summers and not even have to look at or check those batteries or plug them in anywhere to charge them or keep them warm or “care for just like a pet” whether I use the car daily, weekly, or once every two months?  In my entire multi-decade lifetime, I’ve replaced my “neglected” car batteries less than a half-dozen times.  When I became disabled seven years ago, I purchased a small electric cart with “sealed” (AGM?...Gel?) batteries.  I drive the cart outdoors about twenty-five feet to reach my car and then, after shopping, I make several trips unloading groceries from the trunk into the house.  Inside, I pull the retractable cord out of the cart and plug it into a standard outlet until the solid red light blinks, indicating that its ORIGINAL battery is charged.  Problem is that this cart claims a ground clearance of 3 inches but, when the snow accumulation in our northeastern state exceeds 2 to 3 inches (nothing worth clearing off a long driveway and handicap ramps with a pickup and attached plow), this cart can’t navigate more than a dusting without getting stuck from snow buildup under its floor pan.  Tired of being a winter prisoner in my home, I wanted to purchase one of the newer Heavy Duty electric mobility scooters with ground clearance from 5 to 7 inches but those are too wide to bring in through my door and they would have to sit outdoors, albeit right next to an electric outdoor outlet.  The manufacturers of these scooters tell me that I either have to keep the scooter indoors where it can charge in the optimum temperature range above 32 Fahrenheit…OR I have to bring their intolerably heavy batteries inside to charge and store…and I can’t even life a 2-1/2 gallon can of gasoline anymore.  On Thanksgiving of this year, I became aware of the “utility” versions of electric golf carts that claim to be functional for hunters and farmers and other OUTDOOR uses.  I’d expect vehicles designed for outdoors to be able to navigate a couple of inches of snow just to travel down the driveway to the mailbox and back in the winter.  I also assumed their battery-of-choice (whether flooded-lead, AGM, Gel, or lithium ion) could sit outdoors next to the electrical outlet where it could be charging to its heart’s content in winter with temps mostly in the twenties, teens, or single-digits, but apparently I’m wrong.  I can’t get a wide golf cart into the house; I don’t have a heated or unheated garage or shed; I could buy a battery warmer or glow-plug if such an accessory exists for these vehicles but I can’t find one.  What is so delicate about the battery options for electric mobility scooters or golf carts that they can’t tolerate sitting outside and remain functional in our winters LIKE MY CAR AND ITS BATTERIES?!  I have a real need (not a whim) for something that I can envision but, to my surprise, probably doesn’t exist….either not invented yet or not manufactured because there is only an unprofitable niche market for it.  I’ll be long gone by the time power to scooters, golf carts, motorcycles, boats, automobiles, etc. will be provided by an environmentally-clean, recyclable nuclear pellet that weighs nothing, takes up no space, operates in all conceivable temperature ranges, and lasts for eternity.  Seriously, is there no current adequate solution to this kind of battery/power problem related to normal winter temps?

On December 14, 2014 at 5:11pm
Nils-Ove Halvorsen wrote:

There is a big difference in a boat vs car, don,t think your car is grounded like a boat, and connected to shorepower for charging. You know pumps and things on memory or stand-by…. so there is where my experience is. not batteries in cars. For me thats just like a flashlight, change when it runs out… but In a boat with 500-1000Ah It will cost i one gets damage… Good Night, Folks !! Greetings from Norway grin

On January 3, 2015 at 9:27pm
J. T, Crow wrote:

I just replaced the battery in my 2004 Mazda Miata, which was the original OEM battery (I bought the car new).  It was a Panasonic AGM, located in the trunk.  That was ten years of service, during which I accidentally ran the battery dead twice.  I replaced it because it was cranking more slowly, winter is here, ten years is a long time, and I intended to keep the Panasonic on my workbench as a utility high current source.  I replaced it with a similar AGM, since the Panasonic was not available.  The local Mazda dealers now replace the Miata batteries with a common free liquid electrolyte battery (it’s just as good!), which I will not put in my trunk. 
My experience seems to be quite different than in most of the comments above.  The car is garaged in Albuquerque, NM so is not subject to very low or extremely high temperatures.  The car is driven frequently, but not daily.  I measured the idling charge voltage at the new battery as 14.7 volts, unusually high for a car charging system.  I had not previously measured the charging voltage.
I have read that AGM batteries are adversely affected by high temperatures when charging, so I am not sure that I will replace the battery in our other car (which is in the engine compartment) with an AGM battery.  Maybe I will measure the temperature at the battery this summer and decide.
One person’s experience, but I am certainly impressed by ten years of service and complete recovery twice from total discharge, which has killed more than one battery for me in the last 40+ years.

On January 12, 2015 at 9:59pm
Ray G. wrote:

I am thinking of buying a supposedly OEM Mercedes Benz AGM battery which was used as display only but never actually used.  The seller said he had actually had it professionally tested with the proper equipment and the result showed that the battery is in excellent shape. 

The Mercedes Benz dealers sell this type/size of battery for almost $400 here in British Columbia, Canada.  Seller is offering it to me for $180 - of course no warranty and I still need for it to be installed, so additional cost to me.

May I request for your advise on whether or not I should buy it?  What should I watch out for?  Thank you.

On January 12, 2015 at 10:19pm
John Douglas wrote:

Depends on how old it is, what temperature it was kept at and if it was kept regularly charged.
If the Battery was “professionally tested” then surely said seller would have an official document printout with all the information of the testing.

if not, then I’d steer clear.
in low temperatures, AGM’s have a fairly decent shelf life, here in Australia, where summer days are generally around 40c. AGM’s do not fare so.

On January 12, 2015 at 10:55pm
Ray G. wrote:

Thank you for your very prompt response and advice, John.  I really appreciate it.

I was told that the battery is about 8 months old and never been used/installed in a vehicle. It has been a merchandise display on the shelf in a auto parts store which has now closed.  I still have to find out if it has been regularly charged and have requested a copy of the battery test report which supposedly contains data on the “state of Health” and “State of Charge” among other information. Vancouver’s average maximum temperature is 6°C/43°F in January and 22°C/72°F in July.

On January 20, 2015 at 2:20pm
charlie.h wrote:

I just replaced my old Life Line AGM 300amp 6 volt were in my boat for16+years

On March 5, 2015 at 10:56am
keynon young wrote:

Does the AGM battery have lead in them the same as the old style lead core battery?

On March 5, 2015 at 4:47pm
John Douglas wrote:

Yes Keynon, all current batteries except the super expensive lithium batteries are all lead / acid chemical reaction batteries.

On March 9, 2015 at 7:56am
Diego wrote:

Hi John. What about Silver-calcium / acid batteries. Do they contain lead too? I´ve founded some info over there but it is not clear.

On March 9, 2015 at 6:24pm
John Douglas wrote:

Yes Diego, Silver.calcium batteries re still lead acid.
“Grids are still made of Lead. Typically less than 0.1% of calcium is needed to give strength (note calcium is added to the grid alloy in both calcium and hybrid batteries). Some customers think that calcium batteries are completely different to lead acid batteries, but they just represent another generation of the lead acid battery.”

On April 7, 2015 at 6:28am
Dieter Schmied wrote:

I had a question about the difference between group 47 and AGM , so I submitted the question and got this result:

If the above link still works, I wonder why the vile answers from some that surely know more than I but less than the whole truth. My Saab is supposed to have this AGM battery according to at least one supplier. There must be a reason.

PS. I like this site.

On April 7, 2015 at 6:38am
John Douglas wrote:

you auto manufacturer will have a suggested type of battery due to your alternator, which charges your battery and powers the electrics while running.
be careful what a supplier says, check with the vehicles manufacturer to be absolutely sure.

different types of batteries have different charge rates and different float charge voltages.
AGM being a higher charge rate than a standard lead acid batter, the extra voltage will damage a standard battery (but over quite a long period of time)

that’s that basic explanation of why they suggest “x” type of battery.

as for vile answers, well, there are just arseholes in this world that get excited over the silliest things wink
and well, being deep into computers, I can understand when someone gives blatantly incorrect information to people who don’t know better, sometimes it can end in tears and damage.
but one *should try* to remain somewhat civil, but bad moods can get the best of us from time to time, est advice I can give,  you can’t control how other people act, but you can control how YOU act.  wink

On April 7, 2015 at 6:56am
Dieter Schmied wrote:

The information offered about the charging system is well taken, but it may be over my head at this time.

If I am not mistaken most charging systems cahrge at slightly high that the stated voltage of the system (12v would charge at almost 13 volts). When the battery is at full charge, the circuit is cut off to prevent overcooking the battery.

Are AGM systems different?

On April 7, 2015 at 7:12am
John Douglas wrote:

it would depend on your alternator I’d imagine, it varies with different vehicles and different countries with different temperatures..

generally, float charge (maximum charge) is 14.4, but that’s for standard lead acid types,it probably varies with AGM.
seems to give a clear(ish) outlay of info.

On June 15, 2015 at 5:34pm
Martin wrote:

I have a new 100 Ah Ritar AGM battery on my small yacht. It is charged by the 9.9 hp Yamaha outboard motor,and 80 W solar panels.It is oversized for stsrting and lights, to run my CPAPsleep apnoea machine overnight..How low should I let the voltage drop before recharging,and what voltage should Irecharge up to ??

On July 12, 2015 at 6:05am
Toronto X5 wrote:

Hi I am new here. I have a BMW X5 with an AGM battery. I had an very intermittent high voltage issues while driving. Changed the Alternator that has a built in regulator that got replaced with the new alternator. I replaced the AGM battery couple of years ago and no issues with cranking at any time and the battery was always charged.

When ran a diagnostic program again I found the voltage shot up very briefly to 17.8V. I am suspecting the AGM battery causing the alternator to draw this voltage. Can someone advice please

On July 12, 2015 at 7:45am
John Douglas wrote:

Toronto X5 I’d be talking to an auto electrical specialist if I were you, an alternator should never dump anything like that voltage to a battery.
could be a faulty regulator in the alternator.
you could also send an email or ask bmw on their facebook page.

Martin if you want maximum life from the batter, no lower than 12.4v
max charge you’ll find somewhere on the site, bus a fully charged AGM is ~13.4v or there abouts.

On July 14, 2015 at 4:34pm
Doug W G wrote:

Hello, we have a new 27’ travel trailer and the G27 flooded battery it came with seems to be very low quality, has a problem holding a charge over 2 - 3 days of dry camping, can not find much info on it as it is a no-name “Canadian” brand. We are considering moving up to a G31 AGM that has 100 Ah, 220 reserve and 1370 Crank amps. What advantage would we see with the AGM over a lower price flooded with similar specs? I get the no maintenance thing but not sure if we will get more discharge, longer time between charges, etc.? Thanks for your help.

On July 14, 2015 at 5:22pm
John Douglas wrote:

No real difference at all.
the difference is weather it is a standard battery or a deep cycle battery (which have much bigger lead plates inside to allow deeper and more aggressive discharges)

this still doesn’t change the issues though.
1)  discharging below 12.4v (starts to at 12.2) damages your battery, the lower the charge the more the damage
2) cold crank amps are batteries rated for starting engines NOT camping and regular discharging.  get a deep cycle battery buddy.

the advantage of agm, both starting and deep cycle, is that you can’t spill acid anywhere.

On August 19, 2015 at 8:56am
Arkady Mirvis wrote:

I , a retired American living in Portuga, but wit many friends in USA and able to ship a charger, will be greatly indebted to anyone who will point me to source where I can purchase a smart charger for 3 AGM VARTA batteries ( each of 105 Ah ) connected in parallel.
At total capacity of 315 Ah the batteries are installed in my camper to serve my wife’s appetite to ran Toshiba 17” laptop for long hours.
Thanks in advance. An email to arkadymirvis@gmail.com will be very appreciated

On August 20, 2015 at 11:34am
Jim Holman wrote:

I have a 12v 12amp AGM that I charge after every use.
  If I don’t use it for a month and put in on a charger it shows fully charged.  And seams to work like it is fully charged.  Why is it not discharging while sitting for a month?  I run it down each use pumping water.

On August 20, 2015 at 11:40am
Jim Holman wrote:

Sorry. seems.

On August 22, 2015 at 8:21am
Allan wrote:

I have two spiral cell batteries that are well over 15yrs old and still performing well. They have been in daily use and suffer temperatures from -35 degrees C to plus 40. lived to see there way in to their fourth Land Rover Defender all of which have gone to the Sahara every winter, where vibration kills cheaper batteries. The high initial cost has been paid back many times over due to their long and dependable life.
Someone once said to me a battery is a battery after purchasing a new one, why buy a new one then? keep using the old one is what i say.

On August 24, 2015 at 10:10am
Donald wrote:

Here in South Africa we are experiencing power outages on a regular basis. Normally for about two hours at a time. Called Load Shedding. I am looking to install a battery back up system to run a TV Computer and a few lights. That is it. I am not sure what battery would be best. An AGM or a standard deep cell battery. I need performance but longer life is very important too. Any advice would be appreciated.

On September 2, 2015 at 4:37am
Robert Haulin wrote:

First of all i have no idea where all the rude inconsiderate people come from ,,that bash web sites,,if you don’t like what is said hit the delete button.
well back to the facts,,all i’ve read and studied on the web,, the older acid flooded batteries have much thicker cells than the agm,, the agm needs many more plates to get the cranking amps up,, a deep cell battery has much thicker plates-agm plates are on the average of .040 thick-storage batteries are .110 to .180 and golf cart-forklift batteries are .250 area,,the agm batteries need not over 10 amp charge for long life,, plus need a [smart] charger that turns off in float mode then on in @ 80-90% charge. that’s why the short life on most agm batteries,, you need the proper charger for your size - type batt. the old transformer type chargers even on trickle produce too much heat for the agm batt. even 1/2 amp.. Thanks for listening.. If your a jerk-site basher push the delete button.. Doubt if site bashers are even potty trained..

On September 2, 2015 at 5:03am
Robert Haulin wrote:

Forgot that heat is another cause of battery failure,,ideal batt temp is 77 deg.s , heat kills them,, also too fast of a charge destroys the battery,,that’s why they want a slow charge and the electronic regulated chargers intermittently charge,, plus if you leave charger on all the time even 1/2 amp. builds up heat on plates and warps-cracks the plates,also while this process is going on the thin separator plates are destroyed.. if you have room for a larger storage battery that has enough cranking amps. last much longer with the right charger..
sorry for some duplications.. Thanks for all the quality sie responders,great site.

On October 18, 2015 at 1:40am
John Douglas wrote:

“Jim Holman wrote:

I have a 12v 12amp AGM that I charge after every use.
  If I don’t use it for a month and put in on a charger it shows fully charged.  And seams to work like it is fully charged.  Why is it not discharging while sitting for a month?  I run it down each use pumping water.”

that’s because it takes months and months for a battery to start showing it’s parasitic discharge, you only really need to trickle charge for a night, once every six months, make sure to keep stored batteries as close to 25°C (77°F) as possible
as each 8°C (15°F) raise in temperature cuts the life of a sealed lead acid battery in half.

On November 2, 2015 at 8:41am
MJ wrote:


On December 5, 2015 at 11:55am
Ron wrote:

I need real info from real users. I do not like to hear from bearded pencil pushers with stats. Most are changed or updated later when it’s reversed engineered to figure out why they were wrong on paper.. In the real world I see optima yellow or red top batteries as junk. Good for a year or so on diesel truck then it turns over for 2 seconds and starts to click. . In the automotive world I would like to know real experiences. Don’t much care about stats. I want the engine to start so my family gets home safe. Argue stats and get your grants but us normal people need to work and be safe.

On December 11, 2015 at 4:16pm
Brian wrote:

I need a battery that can be inside my van with no ventilation as oer mounted under the hood. Can anyone reliably tell me if glass matt batteries are safe for this application? And don’t give off gas?
I’m told gel batteries are?

On December 11, 2015 at 4:46pm
john Douglas wrote:

Hey Brian.
yes, AGM and Gel batteries are safe for use in enclosed spaces.
only in serious overcharging situations do they vent some gas.
but that’s not going to happen in a vehicle as the alternator is a set charge rate and can’t go higher.

they can be mounted in any way, even upside down.

On January 3, 2016 at 10:17pm
Mark Learner wrote:

I have a 2003 BMW 735i with 160,000 kms on it & the AGM battery has just come up for replacement, that’s 12 years and 160,000 kms out of one battery.  Yes it’s a bit more expensive, but I’m not complaining.  The battery is stored in the boot and is easy to access…basically it’s a long way from the engine heat…

On January 19, 2016 at 1:58am
lui wrote:

am a bit conflicted with the notion of giving the AGM packs good maintenance. how do u maintain a maintenance free pack?

On January 19, 2016 at 2:03am
john Douglas wrote:

if it’s in a vehicle, you can throw it on a good multi stage (expensive) charger (suited to AGM)  and give it a good full charge every six months.

if it’s part of a storage pack fro off grid solar, it gets a bit more complicated.
have a good read through the AGM section.

On January 22, 2016 at 9:17am
theunis du plessis wrote:

what is the low of discharge on AGM 6v battery ?

On January 22, 2016 at 6:16pm
Michael wrote:

 A battery that is discharged to 11.6 volts regularly and then recharged can expect to get 900 to 1000 charges out of the battery. A properly maintained battery will last many years.
From this document :http://www.kendrickastro.com/lvc.html
For a 6v battery divide by 2 of course,  = 5.8v

On January 30, 2016 at 7:55am
TomD wrote:

It is interesting how on these froums the discussions quickly degenerate to a level of personal attacks. Moreover, many (most?) of the statements are based on popular misconcenptions - humorous, but otherwise useless and sometimes dangerous

On January 30, 2016 at 2:06pm
john Douglas wrote:

Tod, I’m not sure what you’re talking about, what attacks?  I haven’t seen any in this thread, or other threads.
and if posts are based on misconceptions, why not correct them with evidence to support your post?

On February 3, 2016 at 3:17am
John wrote:

I have 1600 AH of 200A 12v AGM batteries in a 48v series parallel configuration.

I run the Ritar batteries mentioned in this thread.

A 200AH 12v battery that sells for $325 each…how can any other technology compete?

I run them no more than 20% of their capacity daily.

Coupled with 11kw of solar panels they will last long enough to pay for them selves.

It’s all about recharging them back to 100% and not constantly under charging them (and not overcharging etc)

My batteries are controlled by a Sunny Island Inverter/charger that KNOWS it has AGM batteries, and that is critical.

If you don’t charge them properly with a charger that KNOWS it has AGM batteries connected then you will ruin them quicker than you expect.

On February 17, 2016 at 5:37pm
Connie Hahn wrote:

My battery maintainer does not seem to work on my new AGM battery for my motorcycle.. What is wrong? It works on my friends battery but his is not a AGM battery.

On February 17, 2016 at 5:43pm
john Douglas wrote:

well, the brand and model number for the maintainer might be helpful for a start.
it might also mean there is an issue with the battery.

AGM, GEL and wet cells have different charge requirements, and not all chargers support all models for a proper charge.

when asking for technical help on anything, you need to supply as much information as possible for anyone to really be able to help much.


On February 17, 2016 at 6:34pm
Connie Hahn wrote:

Reply to John Douglas. The brand is a Battery tender and the model # is 021—0123. the battery is a Duracell Ultra. I just checked the volts and it has 12.8 the instructions with the battery says 12.8 volts is 100 percent charged.

On February 17, 2016 at 6:42pm
john Douglas wrote:

OK, so if the battery reads 12.8 and instructions states that 12.8 is fully charged, what makes you think your unit isn’t working?

am I missing something?

On February 18, 2016 at 7:53am
Connie Hahn wrote:

The Battery Tender Model #021-0123 instructions and lights say 1. Steady Red not charging.  2. Flashing Red charging.  3. Flashing Green 80 percent charged.  4. Steady Red fully charged.  and it has worked that way with all my other batteries. I don’t think it’s the battery tender because it still works like that on my other batteries. My problem, the instruction manual for my AGM battery say 12.8 volts is fully charged and it reads 12.8 volts on my voltmeter. When I hook my battery tender up it just keeps flashing Red,Green,Red,Green etc. Maybe it can’t make up it’s mind to charge or not to charge. I have left on hooked up over night and the same thing Red,Green, in the morning. Any ideas, it must be something different with the AGM. THANKS for your time and trouble. Connie

On February 18, 2016 at 2:43pm
john Douglas wrote:

From the manual (here http://www.batterytender.com/021-0123-man.pdf )

This is abnormal and most likely indicates either that the battery is sulfated or that
there is a poor electrical connection between the charger DC output and the battery posts.

time to take the battery back to where you bought it if it’s still in warranty.

On March 4, 2016 at 11:21am
Don Eilenberger wrote:

When a battery is changed in a modern car - the car dealership supposedly has to be visited to “register” the new battery. I know in my Porsche - the PCM (vehicle control module) can be set for a flooded-cell battery or an AGM. Since the vehicle came with an AGM that’s what I intend to replace it with.

Does anyone know if anything else is done when the battery is “registered” - I have heard rumors that the charge voltage is also changed by the PCM based on the age of the battery.  True/False? I’d rather avoid a dealer visit for a $100 computer hookup to “register” the battery.

On March 4, 2016 at 11:27am
Don Eilenberger wrote:

BTW - I can monitor the voltage via the dash, with a pretty accurate digital readout.

On ignition on - not started - I’m seeing around 12-12.3V, depending on what lights come on (in my garage the full exterior light package comes on - automatic light control).

After starting, I’ll see 14.4-14.8V initially (I assume quick recharging of the power used to start the vehicle.)

After running for a while - I’ll see 13.4-13.8V pretty consistently..

The low standing voltage is what’s encouraging me to replace the battery - the vehicle starts and runs just fine. Leaving on a trip in a few weeks and figured I’d do this before leaving.

On March 7, 2016 at 5:28pm
Harold wrote:

I have spent days trying to decide what to buy to replace a Yausa YTZ14s. I just have not been able to give Google the proper magic words for comparative tests of brands. Or there are none. It is going into a Honda backup generator so I am really interested in lifetime and reliability.

No matter which brand, I see comments (generally anecdotal) saying whatever brand is (incredible - will buy forever) or (what a piece of crap). That includes Yuasa (with crazy prices).

Can you point me to any reliable evaluations to help me select. I am sort of circling around Yuasa, ACDelta, MotoBat (the only one I actually found a test result for but actual specs do not look particularly good)), MotoCross (questionable). There are some that claim to be made by Yuasa to the same specs but a lower price point for resale.

There is a plethora of lies, damn lies, and specs. Not to mention the very few actual manufacturers who make a thousand private labeled batteries.

Any help would be appreciated.


On March 7, 2016 at 5:52pm
john Douglas wrote:

for ANY lead acid battery, you’re going to need charging maintenance, pretty much any chargeable battery type has a self discharge factor, as chemicals change over time.

so regardless of what you get, you’re going to need to charge the battery every now and then to keep it healthy.
the most common recommendation I’ve seen is at least every six months, give it a good 8-10hour charge.
another factor is heat, the hotter the conditions (above 25c) the shorter life span your battery will have. check out the section here on heat.

so, as long as you keep the battery charged, and as close to 25c as possible, you’ll get a good 10 years or more out of it.

On March 9, 2016 at 8:53am
Michael wrote:

25° centigrade = 77° F !
Not the typical high or even average engine compartment. 
We had them on the top of Mountains,  grouped closely together,  in hot concrete and metal buildings.  They dried out.  I was able to rehydrate some of them.

On March 9, 2016 at 2:21pm
john Douglas wrote:

Well, you see, I live in Australia, it’s usually a heck of a lot hotter than 25c here in summer wink

On March 10, 2016 at 6:52pm
Jason wrote:

I purchased a Motobatt (AGM type battery) model: MBTX4U. At the time, my rectifier/regulator on my motorbike was failing, and overcharging (+25 volts and higher), and I didn’t know. My bike was burning through lead acid batteries like every 6 months. Everytime I had to call for a tow and wasted alot of time and money. This happened twice. I thought it was just faulty batteries as the bike didn’t get alot of use.  I bought the AGM battery and installed it. Sure, about 5 months down the track the battery emitted a bad sulfur smell and was boiling. I made it home in home in one piece thanks to the amazing construction of the battery. Which I will buy again after also purchasing a new Regulator for my bike. Thankyou AGM!

On April 12, 2016 at 4:49pm
Mr.Smoke wrote:

Looking to replace the battery in my Mazda 6 with a DEKA AGM battery. I live in Ontario Canada and the car is stored over the winter. We see temperatures of up to 30 degrees celcius during the summer while the car is used. I plan to remove the battery & keep it stored in a warm environment over the winter months. Is it advisable to use an AGM battery under the hood of the car, or is it too hot of an environment for it? Would i need to put a charger on it over the winter before returning it to service in the spring?

On April 24, 2016 at 6:09pm
Not So Fast. AGM can easly NOT live up to it's po wrote:

A (some) POPULAR (brand name redacated) batteries had lasted long up to 10 yr I heard.  But the manufacturers bait and switched those.  CURRENTLY their website shows many recent complaints on their higher price “AGM reliability and longevity” advertised batteries.  The complains typical are: “very dissapointed, was told to expect long life: lasted 1 yr, lasted 2 yr, could have got a cheapo that did better.”

MAINTENANCE:  I personally always had to keep my orig AGM charged at least weekly, assumed it came with 9 yr old bike and after near failure to charge (with agm compat. charger) - got new AGM OEM replacement.  I figured my maintenance worries were over, that occasional charging during winter (i use it during winter charging that way as well) would suffice.

FAR FAR from the truth, I am just a few months outside of 1 yr warrantee on a name brand AGM that costs 2x as much as competition and it can hardly turn over the engine unless I charge it first, and it cannot turn over engine if left to sit but a few weeks or less today.

This furnishes a lack of trust in a “mega process industry” that consumers have no control over and can only trust: because the “ingredients” in these batteries are NEVER listed and if they were: we coul now not trust the listing.  WHY?  Because they are making claims of longevity that are far from true, the consumer cannot trust a darn thing they say elsewise.

Absolute F grade in customer keeping.

I would have paid more than I did I only wanted a long life battery I could trust.  Now I can only be sure not to trust the AGM industry and have to find a different way to buy made in USA.

On April 24, 2016 at 6:12pm
john Douglas wrote:

Dude, I’d be getting my bike electrics checked if I were you.

On April 26, 2016 at 2:09am
Cherree Webeck wrote:

I have bought a Solution intelligent pulse marine battery charger. Is this charger suitable to charge an Absorbed Glass Mat (AGM) lead acid battery EV24A-A ??

The battery is in my off-road camper trailer, which is stationary for 6 months of the year in cold weather.

Thank you for your time.


On April 26, 2016 at 7:42pm
john Douglas wrote:

Bearing that marine batteries are generally AGM, I’m betting it’ll be perfectly fine, if you’re not sure though, email the manufacturer and ask them directly.

On May 6, 2016 at 4:55pm
terry scott wrote:

read all the comments, confusing…will some one pls tell me how to charge my AGM 12vdc battery.

On May 6, 2016 at 6:00pm
john Douglas wrote:

what comments were confusing on what points?
you charge your battery either in a car or you use a battery charger.
it’s not a difficult.
how are you using your battery?

On May 12, 2016 at 11:27am
Andrew Gitau wrote:

I have a 2007 camry which i have changed battery 2 times.while a 2005 bmw 525i AGM has been running for 11 years.drving only 24 miles per week for the last 6 years.AGM batteries are obviously superior.

On May 13, 2016 at 1:58pm
Terry Scott wrote:

How do I recharge an AGM, 12vdc… I am using in on a Motor, it draws 3amps.

On May 29, 2016 at 11:01am
jason chen wrote:

I have 2011 Nissan sentra with lead acid battery, can I replace this with agm battery?
is charging system will be ok? thnaks

On May 30, 2016 at 6:03pm
john Douglas wrote:

you can, but you might want an auto electrician adjust the alternator’s voltage, as AGM has a slightly different charge requirement.

generally it’s not much of an issue, it’ll just slightly lower the life span of the battery.

Terry Scott
“How do I recharge an AGM, 12vdc… I am using in on a Motor, it draws 3amps.”

if it’s not in a system with an alternator, buy a battery charger suited to an AGM batery.
or a 10w solar panel with a 3a charge controller.