What is AGM Battery?


An AGM battery, or Absorbent Glass Mat battery, is a sealed lead-acid battery, also referred to as a Valve Regulated Lead Acid (VRLA) battery. Initially developed in the early 1980s, AGM batteries were created as an alternative to costly NiCad (Nickel Cadmium) batteries and were first employed in military aircraft applications.

Today, AGM batteries are widely used across various sectors, including marine, aviation, emergency lighting, off-grid power systems, and advanced vehicles. They are particularly esteemed for their high reserve capacity, enabling them to deliver a consistent power supply over extended periods.

How Do AGM Batteries Function?

The key to the enhanced performance of an AGM battery is an ultra-thin glass mat, also referred to as an AGM separator. This fiberglass mat is positioned between two lead plates, effectively absorbing and retaining the battery acid. As a result, the electrolyte remains in a dry state, in contrast to the free-flowing state found in traditional flooded acid batteries. The glass mat provides an increased surface area for the electrolyte to interact with the battery plates, facilitating a rapid reaction between the battery acid and plate material.

It’s important to note that AGM batteries fall under the category of Valve Regulated Lead Acid (VRLA) batteries.

So, what purpose does the valve serve?

The electrolyte in AGM battery typically consists of a mixture of sulfuric acid and water. During the charging process, a chemical reaction generates hydrogen and oxygen gases. The battery’s valve functions to retain these gases within the battery, preventing water loss. These gases are subsequently reabsorbed into the electrolyte.

However, when there is excessive pressure, as is the case during overcharging, the valve opens to release the gases. This action equalizes the pressure and safeguards the battery against structural damage.

Also See: What is a Lead-Acid Battery?

Advantages of AGM Batteries

The key benefits are:

1. Extended Lifespan

AGM batteries outlast conventional lead-acid counterparts, often doubling their longevity. They maintain a low self-discharge rate, ensuring durability during periods of inactivity.

2. Enhanced Starting Performance

AGM batteries excel at kickstarting car engines, offering over 60,000 starts, around three times more than traditional batteries.

3. Lightweight and Durable

AGM separators don’t fully saturate with electrolytes, reducing weight and enabling them to endure freezing temperatures without risk of cracking or plate damage.

4. Low Internal Resistance

AGM batteries possess minimal internal resistance, facilitating quick power delivery, a crucial feature for engine cranking.

5. Swift Recharge and Deeper Discharge

AGM batteries have exceptional charge acceptance, allowing five times faster charging than traditional counterparts. They can also discharge down to 80% of their original capacity without harm, compared to conventional lead-acid batteries limited to a 50% discharge depth. This deep discharge capacity suits AGM technology for deep-cycle applications found in marine vehicles and UPS systems.

6. Vibration and Shock Resistance

Electrolyte-saturated glass mats between lead plates act as effective dampeners, reducing movement and vibrations. This results in a battery highly resilient to both vibration and shock.

7. Spill-Proof and Maintenance-Free

AGM batteries need no maintenance, eliminating the need for watering, unlike traditional wet cell batteries. The absorbent glass mat securely holds the electrolyte, preventing spills even in unconventional orientations.

Also Read: What is a Solid-State Battery?

Disadvantages of AGM Batteries

Here are two common drawbacks associated with AGM batteries:

1. Susceptibility to Overcharging

AGM batteries have a lower tolerance for overcharging and high voltage conditions compared to flooded cell batteries.

2. Higher-Cost

AGM batteries tend to be more expensive than traditional batteries due to their costlier manufacturing process. On average, conventional batteries range from $65 to $130, while AGM batteries can exceed $200 in price.

Recommended: Do AGM Batteries Need to be Vented?

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