Guest Blog: How to service AGM batteries. Agm car battery meaning

Guest Blog: How to service AGM batteries

As the AGM battery becomes more popular in vehicles, technicians must be aware of the differences in servicing this battery compared to the traditional lead-acid battery.

For many of you, the AGM battery is a familiar item. Perhaps you have a bass boat with an Odyssey battery powering your trolling motor or a vintage car equipped with an Optima battery. If this is the case, you likely know that these batteries require different equipment when servicing them (sometimes). But for most vehicle and equipment owners, the AGM battery brings more questions than answers and not everyone knows the meaning of AGM. So, we thought we’d take this opportunity to address some of the service implications of AGM batteries, which are becoming more and more prevalent in today’s vehicles.

What is an AGM battery?

First, let’s start by defining what an AGM battery is and why is it becoming increasingly popular in today’s vehicles. The AGM battery (meaning absorbent glass mat) is a modified version of the traditional lead-acid battery, with several construction changes to allow it to deliver improved performance in several areas. These construction changes include the use of thinner lead plates, allowing more plates to be packed into the same battery size, which results in greater power. The thinner lead plates can be used because each plate is wrapped in an absorbent fiberglass mat material, which provides structure to that thin plate, keeps the plates from touching, and creates a medium in which the battery’s electrolyte is suspended. This mat is what gives these batteries their name. Finally, because these batteries do not have liquid electrolyte, or are not “flooded”, they are completely sealed, as opposed to a traditional flooded acid battery with fill caps.

These construction changes result in a battery that is more powerful, more durable, longer-lasting, and better able to handle deeper discharging than a traditional lead-acid battery. This last feature is the reason they have become more popular – their ability to be more deeply discharged without harm has made the AGM battery the battery of choice for vehicles equipped with Stop-Start technology. This technology, as we have all come to experience, turns the engine off with each stop to reduce fuel consumption. Doing so places greater strain on the vehicle’s battery since the vehicle’s systems must remain powered during the stop, and results in the battery getting more heavily discharged more often than happens with traditional system designs. Due to this evolution in vehicle system design, the number of new vehicles manufactured using AGM batteries has increased significantly over the past ten years.

What does this mean for service?

Because the AGM battery features a different construction than traditional lead-acid batteries, there are service implications that result. One of the biggest questions we get from professionals and consumers alike is, “How do I know what type of battery it is?” This is a great question. The good news is that starting around 2010, the battery manufacturers and vehicle OEMs did a better job of labeling these batteries AGM. So, the first place we suggest you check is on the battery label itself. Since these batteries are considerably more expensive than standard lead-acid batteries, their AGM construction is usually highlighted. Second, check the battery model number. Often, it could have a suffix such as.AGM. Lastly, check your vehicle owner’s manual – if the vehicle is specified to have an AGM battery installed, it is often called out there. Also, for shops, check your shop information system. These usually do a good job of identifying the battery type specified for each vehicle.

So now you have identified that the vehicle in question does, in fact, contain an AGM battery. What does this mean for servicing it? Of course, that answer is, “It depends!” We’re not trying to make this harder than it has to be, but it really comes down to what type of service we are talking about, as you’ll see below.


When it comes to jump-starting a vehicle with an AGM battery, whether that vehicle is a more traditional design or is equipped with Stop-Start technology, you should proceed as usual. The jump-starting process is essentially augmenting the vehicle’s starting battery (which for some reason is not up to the task of starting the vehicle) with additional battery capacity. It is a DC-DC connection and the jump starter is roughly the same voltage as your vehicle’s starting battery. So, connect as you normally would, following the proper connection procedure, and attempt the jump start. When it comes to jump-starting AGM batteries, it is very straightforward (unlike other service applications).


AGM batteries are much more sensitive than traditional lead-acid batteries when it comes to charging. This falls into two specific areas: the requirements of the overall charging approach/routine and sensitivity to voltage. Traditional lead-acid batteries are very forgiving and can take a multitude of charging approaches and keep on ticking. Not so with AGM batteries, which want a very specific approach and sequence when it comes to charging. They want a constant current bulk charging phase followed by a constant voltage absorption phase, just like what we deliver with our PRO-LOGIX charging approach. In addition, because they are sealed, they are very sensitive to voltage. For batteries, voltage equals pressure. Since the sealed AGM battery has no means to dissipate pressure, voltages must be precisely managed to avoid over pressuring the battery, which can result in degradation of the plates, which eventually will mean that they can no longer hold a charge. So, when charging an AGM battery, it is critical that you use a charger that is specifically designed for use on AGM batteries. This can mean that it is designated “safe” for AGM batteries or, better yet, has a specific charge setting for AGM batteries, as our PRO-LOGIX chargers do. The good news is that these chargers will charge your traditional lead-acid batteries better as well.


When it comes to testing, it is important to distinguish between digital testing and invasive testing. We’ll get invasive testing (testing with a traditional fixed load or variable load carbon pile tester) out of the way first. For invasive testing, like jump-starting, test the AGM battery as you would test a traditional flooded battery. We recommend using the BCI standard or the specific standard recommended by the equipment the battery is installed in. For digital testing, like charging, it is critical that you use a battery tester that has a specific testing routine for AGM batteries. Preferably, it should have testing routines for the different AGM batteries you will encounter. For instance, our SOLAR BA Series digital testers have specific testing routines for Flat Plate AGM batteries (shaped like a traditional battery) and Spiral Wound AGM batteries. This is because the different AGM constructions behave differently when tested, so, an accurate analysis requires that we have different testing routines for each AGM battery construction.

We get a lot of questions related to this topic and there are many trade publication articles related to it, which tells us that there remains a great deal of confusion when it comes to AGM batteries. We hope that this review of the service implications of AGM batteries helps to reduce some of the confusion and allows you to be more effective and confident when it comes to AGM service.

Information provided by Clore Automotive

Separating AGM Battery Facts From The Myths

Have you noticed more batteries are moving into the trunks and under the seats of some vehicles? Chances are, if the battery is not under the hood, it is an absorbent glass mat (AGM) or gel cell battery. AGM eliminates acid spilling in an accident because it is sealed. They can be installed at odd angles.

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These batteries pack a lot of power for their size and weight, which allows manufacturers to shave off a few pounds from the vehicle. That’s a big reason why they are being found more and more on late-model vehicles. Also, these batteries have a greater reserve capacity to support stop/start systems and key-off functions.

Here are the four AGM myths that you may have heard.

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You can use your regular battery charger on AGM or gel cell batteries.

False. These batteries like to be charged slow and low due to differences in internal resistance.

Many AGM battery chargers have microprocessors that collect information from the battery and adjust the current and voltage accordingly. Some have different settings for charging flooded or AGM batteries. Overcharging can kill these batteries. Also, alternators are not chargers. Don’t rely on an alternator to do the work of a charger. If a battery is discharged to the point that it cannot start the vehicle, use a charger as soon as possible to make sure the battery gets fully charged.

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AGMs and gel cells can be tested the same way as conventional batteries.

False. These types of batteries have lower internal resistance than flooded batteries. Older capacitance battery testers/analyzers may not be able to accurately read these batteries. Most new battery analyzers have a special mode for AGM/gel cell batteries. Old-school load testers might not provide conclusive results.

Using a multimeter to measure the state of charge is not the same as with a conventional flooded battery. After the surface charge is removed, the voltage of an AGM with 100% state of charge might be 13.0-volts. A flooded battery might have only 12.6-volts.

AGM or gel cell battery replacement is the same as flooded battery replacement.

True and False. While the installation of the battery may be the same for the two battery styles, some vehicles require an extra step to tell the vehicle that the battery has been replaced.

Newer GM vehicles have a Battery Sensor Module on the negative battery cable. Ford has the Battery Monitoring System (BMS). Other manufacturers have similar systems. These systems require recalibration with a scan tool if the battery is replaced. If the system is not recalibrated, the alternator might overcharge the new battery and cause the battery to fail soon after replacement.

Some vehicles can perform a self-learn for the battery by measuring the internal resistance of the battery. But often a scan tool can force the procedure so you know there will be no issues with the battery.

You can’t upgrade a customer to an AGM battery if the vehicle originally came with a flooded battery.

False. You can install an AGM battery into a flooded battery application. An AGM battery will give the vehicle more cold cranking power and greater resistance to heat and vibration. However, you never want to downgrade a vehicle that came with an AGM battery to a flooded battery.

What Does AGM Battery Mean? How Does It Work?

You’ve probably heard people say that long-lasting battery life is the pivotal aspect when owning a car. If your vehicle doesn’t have an operating battery or fails to retain any charge, how could you rely on it as your trusted partner on the road?

AGM batteries can supply a significant amount of power for your engine. Nothing seems to beat a car with super strength and outstanding performance.

To ensure that everyone knows what an AGM battery is and how it helps, let us explain this in detail so that you can understand the greatness of using one in your car.

Beyond that, more lesser-known facts about an absorbed glass mat battery lie here. Stay tuned

What Does AGM Battery Mean?

AGM batteries are advanced lead-acid batteries operating based on an “absorbed glass” mechanism. Their work is to deliver more power to satisfy the increased electrical demands of modern automobiles.

Absorbent glass mat batteries (AGM batteries) in cars and trucks have two main tasks: run electronics or store power over the long run, and provide starting amps’ powerful bursts.

They were invented in the 1970s as backup power for computer rooms and telephone boxes. From the 1980s, this type of batteries widespread in multiple vehicles: aircraft, military, motorcycles, and submarines. Primarily, AGM works wonders in modern trucks and cars, alongside energy-consuming devices and exquisite electrical systems.

Indeed, more and more cars use maintenance-free automotive batteries and stop-start battery technology.

How Does AGM Battery Work?

Each battery has a glass mat separator made from peculiar fiberglass materials. It’s responsible for wicking the electrolyte solution (water and sulfuric acid) inside the plates. As such, it keeps the electrolyte solution in a suspended and dry state. The glass mats’ coverage produces more power and speeds up recharge.

Once AGM runs, electrolytes move from the fiberglass mat to the plates, creating full capacity without spilling. This occurs even when the battery case gets ruined or tipped on its side.

The chemical mixture inside AGM includes sulfuric acid, water, and lead. While the power draws, the acid molecules transfer to the plates, leaving sulfate and water. Until the sulfuric acid separates from the solution, a chemical reaction occurs on the plates. This process is reversed while recharging the batteries.

The AGM’s superpower derives from Planté battery technology and top-notch designs. First off, lots of valves hinder evaporated water from oozing outside. Thus, this way helps prevent risks and thus, extend the AGM’s life.

Once you overcharge the battery, too much oxygen and hydrogen gases release due to H2O splits, causing water loss. This increases electrolytes’ acidity, mitigates the chemical reaction’s capability, and shortens the battery’s life. That’s when the safety mechanism kicks off, letting gas escape and alleviating the pressure inside the battery.

What Are The Pros Cons Of AGM Battery?

As fascinating as AGM batteries are, many prefer equipping them for their vehicles. Still, AGM has its drawbacks and advantages. Go for a short analysis, and it would help if you compare AGM with other batteries on the market.


AGM looks like top-notch batteries which require no maintenance during use or watering service. They often stick to off-grid and environmentally-friendly renewable power systems such as solar and wind power.

Overall, with minimal gassing and a unique design, AGM batteries could operate and produce power efficiently. The liquid electrolyte flows freely making the whole battery versatile and powerful.

Also, the separator suspension hinders the vibration effectively. Thus, they’re worth installing inside ATVs, snowmobiles, and other Powersports to deal with uneven surfaces.

They get on well with the most start-stop vehicles. They are perfect for vehicles requiring off-season storage as they keep their charge well, have long battery life, and are resistant to harsh conditions.


First off, AGM batteries only work with the correct battery chargers. And they can’t reach the best performance without a full charge.

Beyond that, they need lots of care. Under or overcharging always weakens the batteries’ performance and life. Overcharge may ruin the whole battery and kill it soon. Meanwhile, undercharging creates excess sulfation on the plates, impeding the full charge ability.

AGM works best under the limited discharge of a maximum of 50% battery capacity.

What Are The Differences Between AGM Battery Conventional Battery?

AGM batteries outweigh traditional batteries (or flooded batteries) regarding recharging speed, lifespan, weather resistance, construction, etc. Here are some advantages that might catch your attention in no time:

Weather Resistance

Thanks to the solid construction, internal resistance, and durability, AGM batteries can deal well with extreme cold and heat. This is an ability that conventional batteries can’t live up to.

Rapid Recharging Process

The recharging speed of AGM is faster, 5 times more than conventional lead-acid batteries. Furthermore, the AGM batteries could hold their capacity longer while not being used. They can also recover if drained utterly.

Longer Lifespan

Because of the peculiar valves, AGM can release exceeding gasses if needed or overcharged, and last their life longer.

Beyond that, the unique construction of an AGM battery makes it stay three times longer than a regular car battery. A durable battery is always a cost-effective choice over the long run that anyone desires.

AGM Batteries Support Starts

In particular, an engine with AGM can start up to 60,000 times, over three times more than a regular battery. The starting process becomes faster and more effective. Indeed, AGM is an outstanding battery replacement if you no longer use normal options.

Advanced Structure And Unique Design

AGM batteries contain plates and separators made from particular fiberglass. On the flip hand, the regular lead-acid batteries are a fixture in trucks, cars, boats, and RVs. Their lead plates and separators inside are all packed in a solid casing filled with electrolytes.

AGM batteries also beat the flooded option as they’re maintenance-free, while the standard battery’s maintenance is compulsory.

Last but not least, AGM possesses the start-stop vehicle technology which interests many drivers.

Shaking And Vibration Resistance

Start process just costs your battery a minor amount of electricity. Afterward, the alternator will then take over to charge your battery. They work together to ensure all car components operate correctly.

Of note, AGM batteries can absorb mats. Thus, they incredibly alleviate vibration and shaking, adapting well to boats and watercraft.


As the plate separators hold the electrolyte, AGM batteries are spill-proof, enabling you to mount them in various positions that flooded options can’t work.

As a spill-proof item, AGM can be transported by road or air easier than the regular one (because of the general regulation).

Generate Power

They also have a more extensive and unique design, generating higher voltage output and power.

Not to mention that AGM batteries push the starting process faster and feature extra power for various devices like fuel-saving start-stop systems, backup systems, cameras, and touchscreens, to name a few. is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites.

What Is an Absorbent Glass Mat (AGM) Battery?

We get it–the thing you’re most concerned about when it comes to your battery is that it gives you the power you need. But understanding the different types can be crucial to selecting the right one to keep you powered up and on the go. While you may be somewhat familiar with an old-school flooded lead-acid battery, you may know less about an AGM battery and the benefits and drawbacks of this style. Or is it better to upgrade to lithium?

So let’s break down the most important things all battery users need to know.

What Is an AGM Battery?

At its core, an AGM is still a lead-acid battery. AGM stands for absorbent glass mat, which refers to the technology these devices use to create power. This fiberglass mat sits between the positive and negative lead plates of your battery. Then, as the name suggests, it absorbs and holds the battery acid. That way, it doesn’t freely flow around the battery.

What’s the Difference Between an AGM and Flooded Lead-Acid Battery?

This absorbent mat design is the primary difference between an AGM and a flooded lead-acid battery. Traditional lead-acid batteries simply use lead plates suspended in the electrolyte solution while the liquid flows freely around them.

As mentioned before, an AGM battery is still a lead-acid battery, just in a different design. These batteries still suffer many of the same problems that traditional flooded lead batteries have but do offer a few benefits.

What Are AGM Batteries Used For?

AGM batteries are best used in starting applications. You’ll most commonly find them in vehicles like cars, trucks, RVs, boats, and other motorized vehicles. They provide intense bursts of power as a starting battery. They can be used for energy storage applications as well, but their cost and poor performance make them a lesser choice for these applications.

Benefits of AGM Battery vs. Flooded Lead-Acid?

So why would someone consider an AGM battery instead of the flooded versions you’ve likely been using for years or decades?

Less Maintenance Than Flooded Lead-Acid

You must open up flooded lead-acid batteries to top off their fluids periodically to maintain the correct balance of electrolytes and water. Without this necessary maintenance, your batteries won’t operate as efficiently as possible and eventually become damaged. There’s no similar requirement for AGM batteries, as they’re sealed by design. This means they’re virtually maintenance-free.

Can Install Non-Vented

You can also install an AGM battery in a non-vented way. You often must vent traditional batteries, as they release gases as part of their normal operation. These can build up with corrosive or even potentially explosive consequences without proper ventilation. This lack of venting requirements means more flexibility for you in installation.

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Can Install in Different Positions

The installation benefits of an AGM battery go far beyond helping with venting. While you must install traditional flooded lead-acid batteries right-side-up to prevent fluid leaks, AGM batteries have no such restrictions because they’re sealed. That means you can install them upside down, on their side, or in any other position without significant effect on battery operation. In a crowded engine compartment or small RV battery space, this can be incredibly helpful in freeing up additional space.

Drawbacks of AGM Batteries VS Flooded Lead Acid

While AGM batteries have many benefits, their main drawback is cost.

AGM batteries tend to cost quite a bit more than flooded lead-acid. This price differential may be worth it if you are using it for the correct application. As a starting battery, this could be very beneficial, but for energy storage, the price increase compared to their performance is not worth it.

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In the below video, Mortons on the Move test AGM batteries against flooded lead-acid and lithium-ion (LiFePO4) batteries. The results show that AGM is not worth its price for storage applications.

How Long Does an AGM Battery Last?

The short answer is it depends. In starting applications, you may find AGM batteries last longer than flooded lead-acid. Generally, you can expect an AGM to last for six to eight years in a starting application.

For storage applications, it’s a toss-up between flooded and AGM. For deep cycle storage applications, it’s not uncommon to see a cycle life of around 300-500 cycles if you charge them fully and regularly. This drops if you let them drain too low or only partially recharge them. This tends to equate to around 2 years of usable life in moderate use.

This is why batteries like our lithium with 5000 usable deep cycles far outperform AGM in every regard.

Are AGM Batteries Worth It?

When considering upgrades to your vehicle, your battery may not always be top of mind. But an AGM battery can provide significant advantages to just about anyone who currently uses a traditional flooded lead-acid battery.

On the other hand, if you are looking to upgrade a storage application, you will want to skip the AGM battery and go straight to the lithium upgrade. In the long run, it’ll be cheaper and much less of a hassle, after all.

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