Blog Car Care Advice Decoding AGM Battery Technology: How it Works + Uses
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Decoding AGM Battery Technology: How it Works + Uses

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From military aircraft to cutting-edge start-stop vehicles, the AGM battery has come a long way! 

These advanced lead-acid batteries have a high reserve capacity and don’t require battery maintenance

But how do they compare with a regular car battery? 
Read on to decode AGM batteries, including how they work, their benefits, and more. 

This Article Contains

What Is an AGM Battery?

The AGM battery is a sealed lead-acid battery (valve-regulated lead-acid or VRLA battery). 

AGM is short for Absorbent Glass Mat, which refers to the battery technology used. Developed in the early 80s, absorbed glass mat AGM batteries were first applied to military aircraft and designed as an alternative to costly NiCad (Nickel-Cadmium) batteries. 

Today, you’ll find AGM battery technology in all demanding applications — from aviation and marine batteries to off-grid wind systems and solar panels. An absorbed glass mat battery is also well-suited to advanced cars with start-stop technology and significant power demands. 

AGM batteries are especially known for their high reserve capacity, which allows them to provide a steady power supply for longer durations.

Owing to these benefits and uses, the dual-purpose AGM battery (starting & deep cycle) market value was $11.69 billion in 2023, expected to grow at a 5.9% CAGR from 2024 to 2033. Eminent global AGM battery players include Clarios, Crown Battery, Exide Technologies, and East Penn Manufacturing Company.

Let’s explore the inner workings of the absorbent glass mat automotive battery.

How Do AGM Batteries Work?

The secret to an AGM battery’s enhanced performance lies in an ultra-thin glass mat (sometimes called an AGM separator).

The fiberglass mats in a sealed AGM battery are sandwiched between a lead plate on each side, soaking up the electrolyte. It absorbs and holds the battery acid. This way, the electrolyte is suspended in a “dry” state instead of the free-flowing form found in a regular car battery (flooded acid battery). 

The glass mat maximizes the surface area for the electrolyte to react with the battery plates, enabling a fast reaction between the battery acid and plate material. 

But why is it also called a valve-regulated lead-acid battery?

The AGM battery electrolyte is typically a mix of sulfuric acid and water. While charging, the chemical reaction produces hydrogen and oxygen. The battery valve stops the gases from leaving, preventing water loss. These gases are reabsorbed into the electrolyte. 

However, the valve vents the gases when there’s too much pressure, like when the battery is overcharged. This helps equalize pressure and prevents structural damage to the battery. 

Next, we’ll explore how AGM technology influences the battery’s features.

7 Advantages of AGM Batteries

AGM technology batteries feature a host of benefits, including:

1. Longer Battery Life

An AGM battery has a longer lifespan than a conventional battery — lasting up to 2x longer. These batteries also have a very low self-discharge rate. So, they last long even when not used actively.

2. Generates More Starts

A dual-purpose AGM battery can start a car engine over 60,000 times — about 3x more than a standard battery.

3. Lighter and More Durable

The AGM separator isn’t completely saturated with electrolytes, and the liquid doesn’t expand as in a traditional lead-acid battery. 

Less electrolyte (compared to a traditional flooded battery) means decreased weight. No liquid expansion means the AGM battery can also withstand freezing. And while you likely won’t get any power from a frozen battery, it won’t crack or damage the battery case or plates.

4. Low Internal Resistance Means Higher Power Output

The AGM battery has a low internal resistance, allowing it to deliver power quickly. This is crucial for a car battery, which provides a rapid burst of power to start the vehicle.

5. Faster Charging and Better Depth of Discharge

AGM batteries offer excellent charge acceptance, which extends their cycle life. The AGM battery can charge up to 5x faster than traditional batteries.

They also have an 80% Depth of Discharge (DoD) — meaning they can discharge to 80% of their original capacity without damage. A conventional lead-acid battery can typically discharge to 50% DoD. 

The AGM battery’s deep discharge also allows it to function as a deep-cycle battery. As a result, AGM technology is often applied to the deep-cycle battery format. You’ll find the deep-cycle AGM battery used as marine batteries or UPS backup systems.

6. Shock and Vibration-Resistant

The electrolyte-soaked glass mats in between the lead plates act like a damper. As the plates are packed fairly tightly, movement and vibrations are reduced to almost zero. This makes the battery highly resistant to vibration and shock. 

7. Non-Spillable and Maintenance-Free

The AGM battery is maintenance-free and doesn’t require watering service like a traditional wet cell battery. The absorbent glass mat between the plates holds the electrolyte in place, keeping it from spilling even when the battery is in odd positions. This allows for greater mounting flexibility and prevents corrosion.

Additionally, because the deep-cycle AGM battery is spill-proof, it’s easier to transport them by air or road. Still, it’s best to follow the handling instructions in the battery safety data sheets. 

Now that we’ve examined the advantages, let’s review the drawbacks.

4 AGM Battery Disadvantages

Here are  some drawbacks of using AGM batteries:

1. Sensitive to Overcharging

The AGM battery has a lower tolerance to overcharging and high voltages when compared to a flooded cell battery. 

2. More Costly

AGM batteries are more expensive than traditional batteries as they cost more to manufacture. On average, a conventional battery costs over $60, but an AGM can be over $250.

3. Selective Compatibility

Not all vehicles are compatible with AGM batteries. Check your owner’s manual to know if it’s the right battery for your car. 

4. Requires Special Battery Chargers

AGM batteries require a slow and stable charge. So, you can’t use a regular battery charger with high charging speeds. You need regulated battery chargers or maintainers with microprocessors that adjust the current and voltage delivered to the battery to avoid overcharging. 

In fact, you may face AGM battery damage if a regular charger or alternator charges the battery with a voltage higher than 15 volts.

Wondering if your car runs on an AGM battery?
Read on to find out.

How Do You Know if Your Car Has an AGM Battery?

The best way to know whether you have an AGM battery is to pop the hood and check the battery label. AGM batteries will have “AGM” somewhere on the label or in the part number. You may also see the words “non-spillable.”

That said, if you notice raised vent caps, you don’t have an AGM battery. 

Next, let’s explore other applications of AGM batteries.

What Can You Use AGM Batteries For?

AGM batteries provide reliable power to support advanced car electronics and accessories.

However, you can also use them as a:

Now that you know the AGM battery uses, let’s go over some FAQs.

8 FAQs around AGM Batteries

Here are answers to commonly-asked AGM battery questions:

1. Are AGM and Gel Batteries the Same?

The gel battery is also a “dry cell” lead-acid and VRLA battery. However, it holds its electrolyte solution very differently.

The AGM battery uses an absorbent glass mat. Whereas, the gel cell battery uses a chemical agent (like silica) to suspend the electrolyte in a gel form. The gel restricts movement, so the battery becomes spill-proof. 

Gel batteries are also less preferable than AGMs as starter batteries due to their lower DoD (75%).

2. Are AGM Batteries Deep Cycle?

AGM technology is used for both deep cycle and starter applications.

“Deep cycle” is defined by plate thickness and not the battery technology, so AGM deep-cycle batteries are used as often as flooded or gel cell deep-cycle batteries.

3. What Are Flooded and Sealed Lead-Acid Batteries?

In a flooded lead-acid battery (FLA), the lead plates are suspended in a free-flowing liquid electrolyte. It’s a wet cell battery, meaning the electrolyte can spill and requires regular battery maintenance.  

A conventional flooded battery often refers to a flooded lead-acid battery.

The sealed lead-acid battery (SLA battery) applies similar chemistry. But unlike a traditional flooded cell battery, the electrolyte in an SLA battery is suspended in a gel form (for a gel cell battery) or held by a glass mat (for a sealed AGM battery).

4. How Is a Lithium Battery Different from AGM?

AGM and lithium batteries have their benefits and drawbacks.

The lithium-ion battery is much lighter, has a better cycle life, and can charge faster than the AGM battery. Lithium-ion batteries also have a flat discharge curve (meaning if you power a torchlight with a lithium battery, the bulb won’t dim as battery power runs out — it’ll just go off).

However, AGM batteries are cheaper to produce, have a higher Cold Cranking Amps (CCA) rating, and are vibration-resistant. 

Note: Cold Cranking Amps indicate a battery’s ability to crank the engine in cold weather. You could consult a mechanic to know what type of battery suits your driving conditions.

It’s also important to know that you can’t just swap the AGM starter battery in your car with a lithium-ion battery, as your charging system probably isn’t set up to charge a lithium battery. 

5. What Is a Start-Stop Vehicle?

Start-stop vehicle technology automatically turns off the engine when the car stops (like at traffic lights or in stop-and-go traffic). 

While the engine is temporarily off, the car battery is the sole power source for all the vehicle’s electrical devices, from stereo to GPS navigation. When the clutch is depressed or the brake pedal is released, it restarts the vehicle quickly and quietly. 

AGM batteries are well suited for such demanding applications.

6. What Is Battery Internal Resistance?

Internal resistance denotes a battery’s ability to deliver high currents without a significant voltage drop. Any current that doesn’t go into the charging transforms into heat, which is why batteries get warm during heavy charging. In extreme cases, a thermal runaway can occur. 

New flooded lead-acid batteries typically have 10% to 26% internal resistance, while a gel battery has around 16%. AGM batteries can have an internal resistance as low as 2% in new batteries.

7. What’s Thermal Runaway?

Thermal runaway is when a battery generates excessive, uncontrollable heat that can dry out battery cells and melt the container. Destruction from thermal runaway can release toxic chemicals and cause electrical fires or batteries to explode. 

Thermal runaway occurs most often in VRLA batteries.

8. Which Is better, AGM or EFB battery?

Both EFB and AGM batteries have their advantages.

An EFB battery (Enhanced Flooded Battery) is ideal for small- or mid-range vehicles with start-stop technology. AGMs are best suited for deep-cycle applications and high-powered, heavy-duty vehicles like electric cars and trucks.

Resolve AGM Battery Issues with AutoNation Mobile Service

As vehicles developed greater power demands, battery technology had to evolve to meet these power needs. However, when it comes to meeting advanced power needs, the AGM battery is currently the best among all lead-acid options.

Facing issues with your flooded lead-acid or AGM battery? 
You can always rely on AutoNation Mobile Service for help. We offer transparent pricing and a 12-month, 12,000-mile repair warranty.

Contact us, and our expert technicians will be in your driveway to lend a hand!