What is an AGM Battery?

In the world of advanced battery storage solutions, AGM (Absorbent Glass Mat) batteries stand out for their unique construction and efficiency.

These batteries, which employ a fiberglass mat to contain the electrolyte between their lead plates, offer several advantages over traditional lead-acid batteries.

Published: April 10, 2024.

The design of AGM batteries not only enhances their durability and safety but also allows for a wide range of applications.

Whether for automotive, marine, or renewable energy systems, understanding the fundamentals of AGM batteries can be key to optimizing their performance and longevity.

What are AGM Batteries?

An AGM (Absorbent Glass Mat) battery is a type of lead-acid battery that uses a glass mat separator soaked in sulfuric acid between its lead plates.

This design allows the electrolyte to be evenly distributed across the battery plates, providing efficient electron flow. AGM batteries are known for their durability, resistance to vibration, and ability to charge and discharge quickly.

They're also maintenance-free and can be mounted in any orientation (except upside down), making them ideal for various applications, including vehicles, solar power systems, and backup power sources.

Wet/Flooded vs. Gel vs. AGM Lead-Acid Battery

Wet or flooded batteries are the traditional type, inexpensive but require regular maintenance and upright positioning to avoid acid leaks.

Gel batteries use a thickened electrolyte, making them less prone to leakage and more resistant to vibration and extreme temperatures, yet they are more sensitive to overcharging.

AGM batteries incorporate fiberglass mats between the lead plates to immobilize the electrolyte, offering superior performance in terms of power density, vibration resistance, and maintenance-free operation, making them suitable for a wide range of high-demand applications.

Each type has its advantages, with the choice depending on specific needs such as cost, maintenance capabilities, and environmental conditions.

Also, due to all differences, wet/flooded, Gel, and AGM batteries have somewhat different voltages.

The Recombination of Oxygen and Hydrogen in AGM Batteries

In AGM (Absorbent Glass Mat) batteries, the recombination of oxygen and hydrogen plays a vital role in their operation, efficiency, and longevity.

During the charging process, water in the electrolyte decomposes into oxygen and hydrogen gases due to electrolysis.

In traditional lead-acid batteries, these gases would escape, causing water loss and necessitating regular maintenance.

However, in AGM batteries, the tightly packed glass mats and sealed design facilitate the recombination of these gases back into water. This process significantly reduces water loss, making AGM batteries maintenance-free and enhancing their safety by preventing gas buildup within the battery casing.

This recombination efficiency contributes to the longer lifespan and higher reliability of AGM batteries compared to their flooded counterparts.

However, one must note that AGM batteries are VRLA (Valve Regulated Lead-Acid) batteries. They feature safety valves that, if the internal pressure increases, release hydrogen and oxygen out of the battery, causing water loss. This water in AGM batteries cannot be added as part of the battery maintenance.

Main AGM Batteries Advantages

Since their introduction, AGM batteries offer numerous advantages over older wet/flooded lead-acid batteries, including:

• Maintenance-Free: AGM batteries do not require water additions, thanks to their sealed design.
• Leak-Proof: The electrolyte is absorbed in the mat, making them spill-proof and safe in any position.
• High Power Output: They deliver high currents on demand, suitable for starting engines and high-load applications.
• Long Life: Designed to withstand deep cycles and harsh conditions, offering longer lifespan.
• Quick Charging: AGM batteries charge faster than traditional lead-acid batteries.
• Vibration Resistance: The tight assembly makes them resistant to vibration, enhancing durability.
• Low Self-Discharge: They have a lower self-discharge rate, remaining charged longer during storage.

One also must note that some advantages of AGM batteries are like double-edge sword - like said before, if the battery is too quickly charged and the internal pressure increases, safety valvels may release gases out, causing water loss, although the water loss is better than the destroyed battery.

Main AGM Batteries Disadvantages

Regardless of how advanced AGM batteries are when compared with wet/flooded lead-acid batteries, they nonetheless have some disadvantages as well.

• Higher Cost: AGM batteries are typically more expensive than traditional flooded lead-acid batteries due to their advanced technology and construction.
• Sensitivity to Overcharging: They can be damaged if overcharged, requiring compatible charging systems to prevent premature failure.
• Weight: AGM batteries tend to be heavier than other types with similar capacities, which might be a consideration for portable applications.

Personally, the main disadvantage of AGM batteries is their higher initial cost when compared with wet/flooded lead-acid batteries.

Main Applications of AGM Batteries

AGM batteries are rather versatile batteries typically used in:

• Automotive Start-Stop Systems: Ideal for vehicles with start-stop technology, ensuring quick engine restarts and energy savings.
• Marine Applications: Used in boats for starting engines and powering electronic equipment, offering durability and leak-proof qualities.
• Uninterruptible Power Supplies (UPS): Provides reliable backup power for critical systems and data centers, with quick charging and high power output.
• Solar Power Storage: In renewable energy systems, they store energy efficiently, supporting long discharge periods and requiring minimal maintenance.
• Campers and RVs: AGM batteries are favored for recreational vehicles and campers because of their excellent deep-cycle performance and their robustness against vibrations and shocks. However, they are being phased out in favor of much lighter lithium batteries.

AGM vs. Lithium Batteries

AGM batteries are known for their robustness, maintenance-free design, and excellent performance in cold temperatures, making them suitable for a wide range of applications including automotive, marine, and backup power systems. They excel in both deep-cycle and starting applications and are resistant to vibrations.

Lithium batteries, encompassing lithium-ion and lithium iron phosphate (LiFePO4) varieties, offer a higher energy density, resulting in lighter weight and smaller size for the same energy capacity.

They have a longer lifespan, can handle more charge/discharge cycles without significant capacity loss, and charge faster than AGM batteries.

However, lithium batteries are typically more expensive initially but can be more cost-effective over their lifetime due to their longer lifespan and better efficiency. They also require more sophisticated management systems to ensure safety and longevity.

For short, the choice between AGM and lithium batteries depends on the specific needs of the application, considering factors such as cost, weight, volume, performance requirements and reliability.

For mission-critical applications, AGM batteries are still a far better choice than lithium batteries - if there is a glitch in the system, the internal Battery Management System (BMS) of the lithium battery will protect it by disconnecting the battery from the system, while AGM battery will continue to operate...