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 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 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 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.

AGM is also making inroads into the start-stop function of cars. The classic flooded type is simply not robust enough and on repeated cycling causes a sharp capacity fade after 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. 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 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). 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

Last updated 2015-08-11


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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?

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.”
http://www.yuasa.co.uk/info/technical/silver-calcium-batteries/

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:
http://www.samsclub.com/sams/auto-group-47-h5-agm-36-mo-free/prod9510084.ip?utm_campaign=bazaarvoice&utm_medium=Default&utm_source=AskAndAnswer&utm_content=Default

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.
http://support.rollsbattery.com/support/solutions/articles/4345-agm-charging
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 [email protected] 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.
  Thx.

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.