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, but cheaper than the gel battery.

Most AGM batteries are mid-sized and range from 30 to 100Ah. They can also be found in UPS, big and small for stationary and deep cycle use. 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

Has less electrolyte and lead than the flooded version


Higher manufacturing cost than flooded 

Sensitive to overcharging (AGM has tighter tolerances than gel)

Capacity has gradual decline (gel has a performance dome)

Low specific energy

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

Table 1: Advantages and limitations of AGM

Last updated 2017-10-11

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Comments (174)

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 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. 

On July 6, 2016 at 2:54pm
Doug Huffman wrote:

FIRST, thank you for BU, I have learned a lot, and refreshed my 45 y.o. USN Battery Charging Electrician fundamentals.

I have a used 2012 BMW with an AGM that I charge weekly about 12 AH (1/2 X peak current X hours) to take advantage of the correlation of cycle-life with average State of Charge.

How can I estimate State of Health given that BMW recommends NOT disconnecting the battery?

On August 22, 2016 at 8:38am
Kent Cotterell wrote:

Recommendation for Navy Doug. Check how much the voltage drops when you turn on your lights with the bike not running. Or put an external load on the battery while checking the voltage and voltage drop. Use a 10C load (approximately 10C) which would be 2 amps on a 20 Ah battery. If voltage holds at 12.2+ under a 10C load you are close to fully charged, 12.0 volts = ~75% charged and 11.4 volts =~ 25%. Apply load for about 1 minute before recording your numbers.

On August 23, 2016 at 11:37pm
edward wrote:

may i ask what is the lowest operating temperature for AGM battery??

On September 6, 2016 at 7:25am
Michael wrote:

In the boat I have, I am about to replace the 6 x GEL 183 Ah batteries with 6 x 140 Ah AGM batteries. They are put in an (almost) sealed box under my bed.

I know it’s worked with the GEL batteries for 15 years, but, is it safe with AGM batteries?

Do they get hotter when charging?

On September 7, 2016 at 1:08am
John Douglas wrote:

Yes Michael, AGM will be perfectly safe for you.
both Gel and Agm vent a tiny bit when being charged hard, but it’s not enough to be considered even remotely dangerous or a risk.

On September 10, 2016 at 12:46pm
Marty wrote:

I have read nearly all comments on this forum.I still have question on AGM batteries firstly I used lead acid deep cycle batteries located under the house I bought.The timber framework showed acid burn marks since the kitchen is located above them and that the batteries looked pregnant from overcharging maybe and possibly too old a friend suggested AGM batteries which I bought they are made in china but what isnt nowadays .My concern is that the supplier on ebay did state that they are 10 years old already Initially the batteries performed really well only dropping down to 12volt at night and in the morning they still registered 12volt running the fridge and house lights and laptop pcs .I have recently bought a new solar 100amp regulator now the batteries are showing down to 11.6 volts my question are the batteries being AGM deep cycle the battery bank being 2500AH is 11.6 volt going to shorten their life and being on solar how could I charge them do I need to find a AGM specific regulator/charger.Thank you

On September 12, 2016 at 5:52pm
John Douglas wrote:

bulging batteries would suggest over charging, in which case, AGM and GEL will vent hydrogen gas.
as for acid burn?  I doubt it, can you link pictures of the marks?

so you bought 10 year old second hand batteries?  and you’re surprised they’re not doing well?  10 years is a long life for a lead acid battery, even in a cool climate. they’re just old and worn out.

@11.6 volts. they are already “flat” or one is and it’s dragging the rest down.
you’d need to load test them individually (after charging) to get any idea of what shape they are all in.

being on solar, no, you don’t need a specidic solar charge controller, almost all of then work with all lead acid types, the more expensive and better ones do have specific settings for AGM, GEL and Wet.
what controller you use depends on how many solar panels you have and how many power they produce and what voltage they output.
and how much money you want to spend.

a basic explanation of the different types of solar controller.
cheap end of MPPT is EpSolar BN series @~$200 start up cost.
expensive midnight solar.

it all depends on your needs, how much you’re willing to spend, how much performance you want, how much solar you have and if you plan on more later.
it’s all very complicated ha.

ALWAYS do your research and shop around, you can very easily spend a LOT of money and not have the right setup and lessen your battery life.

On September 13, 2016 at 11:06pm
clay wrote:

Trying to restore a pair of AGM batteries that were stored in Jetskis for two years.. BikeMaster Trugel. BikeMaster recommends a trickle charge for storage, which did not happen.

The batteries are flat @ 2v & 5V. Anyone know what the acid/water mix percentage is for these batteries? What is the charge rate and voltage?

On September 14, 2016 at 9:32am
John Douglas wrote:

Clay, if you’ve read any of this site, you’d know the answer to that question.
you’re out of luck, you’ve let your batteries die.
AGM are sealed for a reason, Absorbed Glass Matt, there is no liquid acid in them, you can’t add any because of the way they’re manufactured.

lead acid of any type HAS to be kept charged when being stored, be it trickle charged over time or charged every six months at most, up to full capacity.
when left uncharged, they damage themselves until they die.

Sorry for the hard life lesson.

On September 19, 2016 at 5:01pm
Jay wrote:

A little disheartening to see so much derision over BATTERIES… Just the facts and true personal experiences please…
How many charge / discharge cycles can be reasonably expected of deep cycle AGM vs GEL cell @ say… 50% average depth of discharge…?
Thank you most kindly…...

On September 20, 2016 at 12:16pm
clay wrote:


The answer to the question is: 30%sulfuric / 70% Water mix added to the batteries and a 14.4V @ 1.2A charge for 12 hours restored TWO batteries. Charge strength appears to be full. Tested them on an intelligent trickle charger, AND for a full day of JetSkiing with many re-starts. No apparent issues. Not sure if we simply replenished the acid, or water but it worked. The batteries were 2 years old, and went at least 1 year without charging. Lucky? Don’t know. But we were able to bring them back from a “almost dead” condition.

And no I didn’t let them die, the previous owner let them die.

Based on research, the AGM is nothing more than a “sponge” that retains the acid mix from sloshing around. Some manufacturers (Varta, Bikemaster) supply a acid mix to be added to the “dry” AGM batteries.

On September 20, 2016 at 6:45pm
John Douglas wrote:

Very interesting indeed.
I’ve tried multiple batteries over the years and never managed to revive a single one.
so yes, could be luck, it could be the way that particular brand was manufactured too.

but well done indeed Sir, I tip my hat to you. ~thumbs up~

On September 28, 2016 at 12:35am
Irabor Akonoman wrote:

Hello Guys,

I have an AGM 200ah battery which i charge with an inverter from the mains. It used to last 6 hours with the load i use. But now it lasts just for an hour on the same load. What is wrong and is there a way i can rectify this without buying a new battery.

On September 28, 2016 at 4:26pm
John Douglas wrote:

how old is the battery?  what summer temperatures do you get?
what kind of charger is it and it is suited to AGM?
how much load is on the battery?  how much do you discharge it and how long before you charge it again?
there are multiple things at play to consider.

On October 1, 2016 at 12:43pm
Marty wrote:

On September 10 I posted my questions on AGM batteries I need to clarify some points to you John the acid burn that I referred to   was done by old type lead acid batteries that were here when I bought the farm they were bulging and acid level was low however I have continued to use them for 9 years they did drop to as low as 9volts and of course the ac power wasn’t there but since the light were 12volt dc I put up with it during the day the solar worked well and I had ac power but the batteries dropped low only during the night time.Incidentally the old lead acid batteries are still here and are not hooked up but are ona Aussie made Megapulse which I am sure that know about it desulpenates batteries I expect over a long time period anyway its worth a try .Recently about 3months ago I purchased second hand AGM batteries I have a battery bank of 2500AH this batteries have no manufacturing date on them they are manufactured in china and have a label EMERSON they appear for sale on ebay on and of.

On October 22, 2016 at 12:57pm
Andy wrote:

I just want to say I was looking for some info on AGM batteries and came across this site and these discussion.  I appreciate all of the information and experiences shared, it is helpful for me to read the good and bad.
My personal experience is with flooded acid batteries used in gas powered vehicles and motorcycles for the past 50 years. It’s been my personal policy to expect to replace this type of battery without any questions as soon as they get to the 5 year mark.
I live in Ontario and in the dead of winter the temperature at night can get very very low and the first time (when I was much younger) that a battery failed to turn over my engine and I tried to “save” it by charging it and continued to try using it was the last time.
Extremely cold temperatures is a great way to test the capacity of an old battery wink.
Now I have learned that is why we have a Fall season, this is to give people who are unwilling to accept that batteries have a definite limited life one last chance to accept that it’s time to replace thier 6 year old battery, before winter.
So I know it can cost money but sometimes you just have to accept that no matter how well you maintain a battery and the charging system, eventually just like everything in this universe that nothing gets better with age, except maybe wine and cheese?
Batteries have a life and when they start to go it’s time to say goodbye and do the right thing and just let them move on to the afterlife, give them a proper burial and remember all the good times you had together, and move on.

On October 25, 2016 at 4:02pm
Hector Serrano wrote:

i got 10 battery under my bed to power my inverter the is connected to some lights,and i charge whit a solar panel i am disable do to motorcycle accident so i stay long periods of time in my room,my concern is if this type of battery is bad for my health, i having my eyes like dry and achy , the some one know if this battery discharge any gases or any the i need to know , any one please lead me know, i will appreciate any info the you can tell me, tank you you can contact me at www.caserio1027@aol.com   or wassup me, text or call
at 321-443-3855 Hector
Thank you all

On October 28, 2016 at 1:19am
Peter Edward wrote:

As usual, great information from BU and well put.

But shouldn’t the last ‘Limitation’ be an advantage? ie less electrolyte and less lead?

Perhaps a reword would help.



On December 9, 2016 at 7:34pm
Sparky wrote:

I bought 2 new EverStart ABS batteries at wall mart because they were missing parts I only paid $15 each. One is a ES14AHBS and the other is an ES16LBS
They were both missing acid and caps for the batteries. I have tried to find the type acid that I need to use and caps that I need but have had no luck. I learned they were made by Johnson Controls and I emailed them for help but that did not help. Does anyone know where I could buy caps or retro fit caps from like size batteries. Johnson Controls also make also make Die Hard and some others battery brands.
Thank You

On December 22, 2016 at 7:51pm
Adewale Coker wrote:

Still new in the field.

On January 11, 2017 at 12:36pm
Bill Catz wrote:

AGM charge current should be between 0.10 and 0.15 of the20 hour rate AH rating.  So a 100 AH battery should be charged at between 10 and 15 Amps.  This creates a downsiide to AGM use in that it could literally take 10 hours or more to fully charge your battery.  After using AGM and having a big failure, we went with the added expense of a LION battery.  Several advantages over AGM including a better discharge voltage curve, faster charging time and long life.

On January 29, 2017 at 10:47pm
divp wrote:

Thanks for post…worth reading

On January 30, 2017 at 12:28pm
battery yes wrote:

LION is expensive garbage.  Bill Catz you will see very soon that you made an unwise decision and you wont be a dope next time you buy batteries again

On January 30, 2017 at 6:32pm
John Douglas wrote:

care to explain why Lion is garbage?

On January 31, 2017 at 10:55am
battery yes wrote:

why sure.  the Lion battery exhibit a natural degrading effect as soon as its produced, additionally they can explode much easier thus leaving them more dangerous and they are susceptible to being severely damaged when exposed to too much heat and especially so when discharged too much or overcharged.  in addition, morons like you (john douglas and Bill Catz) do not know how to use them properly and will probably not understand the ways of AGM, Lion or anything that relates to life.

On January 31, 2017 at 11:00am
battery yes wrote:

reading this whole string, it seems as though John Douglas is a youtube warrior… gaining all his knowledge from youtube and offering boneheaded advice to people on here about batteries.  John Douglas stick to what you know…


Comments are intended for “commenting,” an open discussion amongst site visitors. Battery University monitors the comments and understands the importance of expressing perspectives and opinions in a shared forum. However, all communication must be done with the use of appropriate language and the avoidance of spam and discrimination.

On January 31, 2017 at 11:10am
battery yes wrote:

how dare the moderator edit what i wrote to John Douglas.  John if you wish to produce your email address, i would be glad to discuss this further with you… thats of coarse if you’re not too busy touching your keister

On January 31, 2017 at 11:40am
John Douglas wrote:

Wow, ask a simple question and you lose your mind?
Yes Lion has a natural degrading effect, but so does lead acid of all type.
yes, they can explode, if damaged and punctured, which is unlikely in a battery bank situation.
and even then, they’re used in all Tesla vehicles which to my knowledge, have never exploded.
and what heat is likely in a battery bank situation?  and in how would they be excessively charged / discharged in a battery bank situation?  charge controllers designed for Lion protect against that.
and how on earth have you possible determined that I know or do not know about such?
which such a infantile response, I very much doubt you do either.
if you did, you’d not go on like a pork chop.
and how exactly have I been a youtube warrior and what has that to do with this discussion page?  seriously, you’re a twit.

On January 31, 2017 at 12:43pm
battery no wrote:

ok guys, This is getting too much for this forum.
It was funny though when he said that John is too busy touching his keister… LOL

On February 1, 2017 at 11:36am
battery yes wrote:

John Douglas going by reading this entire comment string, you have a tendency to respond to people with an arrogant and holier than thou overtone.  most of what you have written here in this string is simple stuff you google.  come up with information on your own or through your own personal experiences.  i trust nothing of what you have said

On February 1, 2017 at 6:26pm
John Douglas wrote:

Good for you, I don’t care what you believe or trust or think you know.
you’ve given absolutely no evidence to support a damn thing, nor have you provided any thing to show where I have given any type of misinformation.
you have no idea what I’ve done or come up with or experienced to state any of your rubbish.
you just make yourself look silly.

On February 2, 2017 at 7:06am
battery yes wrote:

and furthermore… id love to have a battle of wits with you… but, frankly, you are unarmed.
keep doing what you do best…touching your keister

On February 12, 2017 at 5:30pm
Chuck W wrote:

I have a 20 mo. Old Oddesey 12 v. AGM in my Mazda 3.  I charge twice a month with a smart variable rate chgr. I paid $180 online for it. I have reliable starting at cold temps. The Oddesey battery can produce 2600 amps of push in the first 5 seconds, that’s over 3 times more amperage than a same size wet cell can produce.  To me an agm blows away the other batteries! !

On February 16, 2017 at 10:15am
battery yes wrote:

Chuck W… the AGM Odyssey will produce more cranking amps because it is a thin plate battery… the more plates, the more surface area the more cranking amps for a short period.
I bet you John Douglas didnt know that

On March 5, 2017 at 12:15pm
Jeff wrote:

Okay, I’m new to the discussion, and have a question. I’m familiar with the construction and technology regarding AGM batteries vs flooded batteries. My question is this:  I work at an auto auction where on auction day, we have to jump start hundreds of vehicles. We are going to purchase 3 of the Solar commercial battery jump starters, but you need to choose/provide your choice of 31 series battery. I’m stuck between the AGM battery and the NAPA commercial series battery. The AGM comes with a 1 year warranty while the commercial series comes with a 3 year, free replacement warranty. As far as the specs, I know the 31 commercial will put out more CCA, and the outside sales rep said they will allow “deep cycling” as well as an AGM battery. They will be in roller carts, so not a ton of vibration, they will be operating in temps from below 0 F up to 100 F. The price difference is about $45/unit more for the AGM batteries. In my opinion, for the $ difference, and the 3 year free replacement warranty, the commercial battery makes more sense. However the lot ops supervisor disagrees and wants the AGM batteries, even at the higher cost. We will be needing 6 batteries total for these 3 jump starters, so without giving individual specs on each NAPA 31 series AGM or commercial series battery, I was hoping someone could give their opinions as to which battery would best fit our needs. Any and all responses are welcomed. Thanks!!!

On March 7, 2017 at 10:46am
battery yes wrote:

First off, do NOT take advice from John Douglas, he thinks hes the foremost expert on here and he knows nothing.
Second, it depends on what AGM batteries you are looking at.  The Odyssey or Northstar thin plate AGM batteries are the way to go, however they are more expensive than you may think(probably $250 or more each) but are well worth it.  They have the highest CCA available and the best guaranty.  If not, the Napa commercial group 31s will work fine, they are manufactured by Deka (well they used to be, Im not sure of Napa switched as of lately).

On March 7, 2017 at 3:17pm
Ted wrote:

Battery Yes you sound like a real knuckle head that threw fits as a child when you didn’t get your way. FFS, get over it and just stick to facts if you have them, not opinions, too many of those make helpful sites useless.

On March 8, 2017 at 5:13am
battery yes wrote:

The knucklehead is you.  Its funny that you have absolutely nothing to offer on here.  In fact you are the complete opposite as John Douglas.  He at least tries… you were just lured in by trying to make a lame insult, yet you look like the biggest idiot of all.  What say you about starting batteries…?

On March 10, 2017 at 8:19am
PMK wrote:

I’m not a battery expert, but after reading through the comments I can add a little insight based on many years of use.
I have been using AGM batteries for about 15 years both Odyssey and Northstar and have found them to be superior to any flooded battery I have ever used. I work for a very well known theme park company as a manager of prototype development and we regularly use series battery packs to power our development vehicles during testing. Over the last 25 years we have pretty much used every type of battery on the market to include some very expensive lithium/metal versions requiring very controlled charging. Bottom line is, AGM batteries have allowed us to get longer run times between charges due to the higher power density and shorter charge times. We regularly discharge into the 25 to 30% range and charge at rates as high ad 120% of what is recommended. Most of my employees have AGM batteries in their vehicles, not because they bought them, but because they use the ones out of our test vehicles when we’re done with them. I have one that’s been in use for over 8 years after the abuse we subjected it to in our testing.

On March 30, 2017 at 9:00am
dan phillips wrote:

when I read the information printed I thought great those are the ones for me . Then after reading lots of the comments I still do not know whats best for my mobility scooter

On March 31, 2017 at 7:46am
battery yes wrote:

dan phillips, Dont listen to the lot of comments on here (most of which are not well thought out).  From my 34 years of experience thus far of selling and testing batteries.  AGM or an AGM/GEL hybrid performs the best in a mobility scooter.  AGM/Gel hybrids are not really produced now though (although they were by one particular company, they no longer produce batteries anymore).
Also, if John Douglas or Ted replies to your comment, ignore them.  They have proven to be knowledgeable in very little.

On March 31, 2017 at 4:17pm
John Douglas wrote:

Remember kids, he knows boats wink
do tell us all Dan, what experience is that exactly? retail? engendering? the sciences?
chemist? blow hard?
yes kids, listen to this man, he knows his shit, but don’t ask for links, or data or evidence, that’s not his game wink

On April 1, 2017 at 2:37am
Arkady Mirvis wrote:

I bought from Amazon.da a CC-BC -30 made by Einhell battery charger. Only when it was delivered I spotted that instruction forbids use of this charher for AGM batteries. That warning is not given in any advertising. A factory expert stated that CC - BC- 30 is for flooded batteries and AGM max. charge must not exceed 14.1 - 14.3 amperes.
I need a charger for my 3 connected in parallel VARTA batteries 105 Ah AGM batteries. I do not know shallI keep the charger or send it back. Has anyone used CC-BC - 30 to charge AGM batteries.
Reply will be appreciated.

On April 4, 2017 at 2:51pm
MJo wrote:

Recommendations please: Small back up solar system on roof of our house to AGM batteries. Batteries are 3 DataSafe (Yuasa) Batteries 135 amp hour manufactured 2003 lightly used from a telephone switching system. Put into used on solar setup in 2005 and have been terrific! (Lucky us). I use a charge controller, Battery recommendations were to charge 2.27volts/cell or 13. 6 volts float charge. I used a 13.6 volt float charge. New roof installed over the winter (Northern Midwest) and system came down. Battery that the temp probe was hooked up to cannot maintain a charge over 11.8 volts. (Other 2 batteries fine).
1) Does this point to one of the cells of this battery being bad? I have heard you can take off tops of AGM batteries to add fluid, do you recommend it? Or is this battery shot? Does it make sense that one of the cells is bad and needs fluid? (2.27 volts/cell -6 cells = 13.6 volts?
2) Replacement battery: They are not cheap and I have read you should not use a new battery with an old set; is that correct? I would like to keep the same 300+amp hour backup so if this battery is shot, would I have to get multiple new batteries? Thank you for your help on this. Kind regards, MJ

On April 21, 2017 at 11:52pm
Georg O. wrote:

I’ve been running a manuf spec 210 AH AGM 12v battery stack in an rv for three years, solar charging with an 80 AH load every day.

Ive noticed they don’t hold a charge as well as new but the manuf says to replace after 3-5 years.

I use UPG batts. Universal Power Group, chinese origin.

They power a a 120v ac inverter; most loads are 120vac.

If you use your batts to power an inverter as I do, KNOW THIS:

Amp hour ratings are derived by dragging the battery down to 10vdc which is rediculous. I take mine no lower than 12vdc.

Who runs their stack down to 10vdc???

An inverter has a low voltage cut-off at about 10.5 to 11vdc. You should only run them down to 12vdc anyway.

So I consider any manuf AH rating to be TWICE what is actually available real-world especially if you ate powering an ivnerter for 120vac loads.

On April 22, 2017 at 12:04am
Georg O. wrote:

Reply to MJo:

Do not mix and match batteries of different ratings.

Yes, batteries fail. One dud will pull your system system down.

Do not mix and match batteries of different ages.

Do not disassemble batteries.

Right, off grid is not at all cheap; if you want cheap power, use the grid, really.

I install off grid and emergency backup battery power systems primarily,
sometimes diesel and propane gen systems.

Yes, batteries are very expensive. If you lean on them hard, dont expect them to last forevah.

Best to you. Dinkering around with a sealed AGM to tweak electrolyte etc. is a bad idea.


On April 24, 2017 at 9:25am
John Douglas wrote:

MJo, I’d say yes, it’s developed a bad cell, or it’s just had it.
you can *try* and add distilled water, but I’ve only ever managed to bring back two to life out of about 20, and even then, at greatly reduced capacity, which will drag the other batteries down if they’re in a bank and only damage them more over time.

and yes, it’s recommended not to use now batteries with old as they have different capacities and the old ones will drag down the new ones(s).
and yea, they’re damn expensive :/

you could check if you have any battery distributors int he area and see if they have any out of warranty shelf stock you might be able to get at a discount.

Georgg O


one of the most comprehensibly programmable low voltage disconnects I’ve yet found.

On June 11, 2017 at 7:26pm
Horence wrote:

To battery charger, the more that I know about is to use bestek 400w power inverter to charge camera battery when camping outside. The way to handle this tool is to connect with car cigarette lighter charger outlet. If you want to catch more information about this tool, you can search bestekmall on Google. Have a nice day.

On August 19, 2017 at 2:04pm
Jessica wrote:

Sam’s Club installed an AGM car battery for me. 

A few dollars more than non-AGM, but well worth it to postpone the time when some freezing-cold morning, my car doesn’t start.

On September 13, 2017 at 12:01am
hasan wrote:

i would appreciate if anyone help me about following question: what is difference between agm separator for different application such as : solar, Ev, ups, motorcycle and start-stop?

On September 13, 2017 at 8:35pm
Jeff wrote:

From what I’ve been gathering this AGM battery can be mounted on it’s side.  And, if in storage it should be fully charged every 3 months.  Advantages,  it’s less vulnerable to vibration plus its lighter than a traditional, flooded lead acid battery.  However heat can be an issue to longevity.  (extreme temps +120 Fahrenheit).

On November 5, 2017 at 3:57pm
Edmund Dontes wrote:

Some people are compelled to comment as if they’re the smartest person in the universe. Incredible…

On November 6, 2017 at 4:07pm
John wrote:

No one has commented in two months, did you need to feel special and want some attention?

On December 20, 2017 at 5:15am
Nikki wrote:

I have just bought 22Ah AGM batteries for my mobility scooter. Could someone please tell me if it is possible to take on an Siri plain asi travel quite a lot.

On January 11, 2018 at 10:43am
Carlos Peña wrote:

las baterías shuriken sk bt20 son de gel o acido…..............?

On January 12, 2018 at 4:10pm
español wrote:

CarlosPeña > son tres tipos de bateria: acido, gel y agm . ese shuriken es AGM

On January 15, 2018 at 3:52pm
wise guy wrote:

AGM batteries require specific voltage and current to charge them properly,  thus there is a special AGM (or winter)  mode on battery chargers, eh?

So tell me how a car/motorcycle knows that the user just replaced factory lead acid battery with AGM ???  Obviously it charges it as it would a regular battery,  thus shortening its life.  I paid like 3x more for Optima red top.. just for bling because it failed after 1 year,  and i mean totally dead.  While my regular Varta is still alive after 10 yrs believe it or not!!!

On February 1, 2018 at 7:59pm
Jim wrote:

I have 8 brand new AGM Deka 8A8D 12-volt batteries for two parallel strings of 48-volts. This is used in 65F basement for solar storage. Each about 250 Ah.  Off the truck they measured 12.91 volts, exactly the same. However, when charging them for first time, and watching/measuring each battery of 4 in the string for excessive voltage, one battery stayed at 13.8 while others made up difference of little higher than expected. on even 15 or so. I terminated immediately. Is it the varying internal resistance causing the uneven voltage drops across the batteries. East Penn who makes them, says not to exceed 2.43 volts per cell max (14.6 volts), even for an equalization. I charged the lower battery for few hours at 1.2 amps and tried the 48 volt charger again. The low “problem” battery now climbed to16 volts, while others now lower at 13.8. What will it take to even out these voltage drops so as not to damage 5000 dollar investment? Will it require a discharge first, to even them up?

On February 10, 2018 at 5:47pm
Andrew P wrote:

Jim, you will want to connect your batteries up to an equalizer such as this one http://amzn.to/2nRe2XE
It is the only device I know of that will maintain even voltage across batteries setup in a bank.

On February 17, 2018 at 10:00am
Mobin wrote:

hi everyone,
I have a new sprinter xp12v 2500 69AH AGM battery, and 100 watt solar panel, i have tried both 20A MPPT charge controller and 10A PWM charge controler, but couldn’t get enough charge out of battery,
I use only 2 light with maximum 2amp of usage at night, but my battery only last 5hrs. Is there anything wrong with my charger or am i charging my battery in wrong way?
Even noticed that MPPT chargr controller only charge battery at 1.5-1.7 amp out of 6 amp of solar power.
I have consulted solar dealer in my country, but no one could give me a proper solution.
Any help would be appreciated

On February 24, 2018 at 5:53am
mah wrote:

What should be the best charging routine for the 24V (2x12v)/28AH battery of my wheelchair ?  with a full charge I can go 20km/12miles but I mainly use it at home and with my usage, the battery charge would last for almost 2 weeks. But I know that deep discharging would decrease the life of a SLA battery. Is it okay for me to charge the battery every week or should I charge the battery daily ?. Please suggest the best possible routine for charging the batteries so that I could get most out of the battery and also increase the life of the battery to the maximum extent possible.

On February 26, 2018 at 12:25pm
Recharge wrote:

Charge it every day, that way the battery is kept in top condition, you can’t overcharge a lead acid with a charger, it’ll just keep it at float if it’s full.

this will give you the longest life possible.

if you’re worried, add a digital volt meter and charge it when it gets to 12.4v, that way you’ll never over tax it.

but again, charging every night is the best possible option.

On February 26, 2018 at 12:31pm
Recharge wrote:

Mobin, best way to be sure is to charge the battery for 8 hours on a standard charger, let it sit for 8 hours and then check the voltage, if it’s below 12.5v it’s buggered.
if it’s not, connect one of your lights and then check the draw voltage.

https://www.caravansplus.com.au/guides/calculating-how-big-your-battery-needs-to-be-a-44.html   will give you some information.


On March 15, 2018 at 7:24am
Jeffery Tansey wrote:

I would like to know if I can charge a 12v14ah battery with a 1.8 amp charger.

On March 15, 2018 at 9:26am
Recharge wrote:

if it’s a 12v charger, then yes.
the Amp rating is just how fast the charger can charge the battery.

On August 23, 2018 at 5:58am
Micko wrote:

Hi.  I recently installed a fullriver DC20-12 in the back of my Nissan patrol that will get charged via the alternator when driving and solar when camping. So when I’m driving the voltage at the battery reads 14.3 to 14V with 4.5 amps going in when my fridge is running which then drops down to 1.5 amps when it has reached temperature and turns off.  Would this be to high a voltage if driving for 8+ hrs?
The specs on the battery say cycle charge is 14.5 - 14.9V and float 13.6 - 13.8V. I’m not worried about short trips but would like options on the longer ones.

On August 29, 2018 at 4:06am
Scott Marshall wrote:

Micko, I have a similar setup and installed a solenoid between the AGM and the charging system. It’s wired thru a switch (on-off), so the battery can be set to disconnect from the vehicle (if you run it down during camping, the starting battery is preserved so you won’t be stranded. In the ‘on’ position (auto), the switch connects the solenoid to the Accy circuit, so charging begins as soon as you start the vehicle. In the other, it disconnects the AGM so when it is fully charged you can stop the charging.

This has worked well for me on several vehicles over the years.
You can find the solenoid and switch on ebay or amazon. The solenoid is about $20 - be sure you get one designed for constand duty, not one designed for starting - they looks similar, but the starter duty on will burn out in a few minutes, as it’s designed only for cranking.

Good luck!

On August 31, 2018 at 5:33am
IHSA wrote:

I have a new Alfa Romeo Giulia with a VARTA AGM battery. The battery packed up after 18 months. I went from my home, parked the car, and the battery went to totally dead in about 2 hours. I again bought a VARTA AGM which is very expensive, so when this second one goes I will buy a normal sealed lead acid battery - they also last 18 months to 2 years, and is half the price.

On September 21, 2018 at 12:02am
Ken wrote:

Can you tell me what would be the typical charging current for 315Ahr battery bank of AGM batteries at say 25deg C when in float mode @ 13.8V
I understand this will vary with age, self discharge, gas recombination etc,etc but I am just looking for some idea of what to expect.

On November 7, 2018 at 11:12pm
ELLIOT wrote:


On January 8, 2019 at 3:50pm
Nick wrote:

My Optima AGM battery in my corvette has a lifetime warranty. That’s all I need to know. Sometimes when I leave it in the garage all winter with the radar I kill it. I have to charge to 45% and then burn it past. I’m happy with it over regular batteries.

On January 31, 2019 at 9:03am
chad wrote:

Do I need a different kind of maintainence charger for my AGM than led-acid?