AGM Battery

An AGM (Absorbed Glass Mat) battery is a type of VRLA battery (Valve Regulated Lead-Acid) that contains fiber-glass mat separators which has absorbed an electrolyte fluid. These types of batteries are also known as sealed lead-acid batteries. Although they are sealed completely they will typically contain some kind of pressure release valve to prevent them from cracking or exploding.

Unlike vented batteries, an AGM battery won’t spill it’s conductive solution when tipped upside down. They contain much less battery acid (electrolyte) than a standard vented battery (like a car would use) which has given them the nickname acid-starved. This makes them somewhat safer to handle and store than a traditional vented battery.

How Valves Regulate Water Loss in AGM Batteries

Vented batteries allow the gases formed from use to escape the battery. This is why standard vented batteries must be refilled periodically. Valve regulated batteries force the oxygen and hydrogen produced in the battery to recombine to create water that’s then absorbed back into the glass mats. Since the batteries aren’t vented you never have to add any water to them.

AGM Battery Advantages

• Smaller Footprint – An AGM battery takes up less space than a traditional flooded (vented) battery. Their design allows them to store more power in a smaller space.
• High-Rate Capacity – AGM batteries are able to provide a lot of power fast. This is why they’re used for UPS applications (Uninterruptable Power Source) as they can provide enough power for many devices.
• Mounting – Because the valve only functions in high pressure conditions, you can mount these batteries anywhere, at any angle without worrying about them leaking.
• Less Ventilation – With a large bank of AGM batteries you don’t have to worry about ventilation like you would with a large bank of standard vented batteries. No dangerous acid fumes are ever emitted during normal operation.
• Safer – There’s much less risk of being harmed or doing damage if the case of the battery is compromised. This makes these batteries much safer to own and operate. You don’t have to worry about splashing battery acid everywhere and you don’t have to worry about them leaking either.
• Low Maintenance – Since you never have to refill them these batteries are much less maintenance. You almost never have to inspect them or make any changes to them at all over the course of the battery life.
• Purer Lead Plates – The lead plates aren’t required to hold themselves up so a more pure lead plate can be used. This leads to a higher power density.
• Low Resistance – The lower resistance found in AGM batteries allows them to be charged and discharged much faster than a standard vented battery.
• Vibration – Due to the sandwiched plate design of AGM batteries they are much more tolerant to bumps and vibration. Not only that but you don’t have to worry about them leaking if their cases get cracked once they’ve been bumped around.

AGM Battery Disadvantages

• Pressure Release Diminishes Capacity – Once a pressure release valve in the battery is forced to release gases the battery loses some capacity permanently. Unlike flooded batteries you can’t just fill them back up.
• High Temperatures – AGM batteries are much more sensitive to high temperatures than traditional flooded batteries.
• Thermal Run-Away – These batteries are much more susceptible to complete thermal run-away if they are being abused while charging.
• Cost – AGM batteries are about twice expensive as their flooded cell counterparts on average.
• Over-Charging – Over charging your AGM battery can lead to gas discharge which can diminish the capacity of the battery.

History of AGM Batteries

The very first AGM battery ever created was known as the Cyclon. It was originally patented by the Gates Rubber Corporation back in 1972. Gates Rubber has since become Enersys. The Cyclon got its name from the spiral cell with foil electrodes.

Manufacturers seized the opportunity to work with this new battery technology and began incorporating the design with their own battery cells that contained traditional flat plates. In the early 1980s a company known as Yuasa gained a considerable market share by selling AGM batteries for the purpose of emergency lighting and alarm systems.

In the mid 80s the AGM battery took center stage in Britain with the advent of a British Telecom specification for batteries to power their new high tech digital exchange network. Around the same time Gates, the original creator of the AGM battery, bought another battery company in the UK that specialized in aircraft batteries. They used their Cyclon design to create a battery which was soon adopted for use by business jets, F16 fighters and even the legendary Harrier.

What is an Absorbed Glass Mat?

AGM batteries are a lot like traditional lead acid batteries you find in cars except that the electrolyte material isn’t allowed to flow freely. Thin glass fibers are woven together to create a mat that will maximize the surface area available for the electrolyte material. After the fiber-glass mat has been woven and soaked with battery acid it is then sealed to hold all the acid in.

These absorbed glass mats are then placed in between metal plates to create the AGM battery. These plates may be flat, slightly bent, or wound. Most AGM batteries are contained in a rectangular case as per the BCI battery code speficiations.

Common AGM Battery Applications

• ATVs – Since you don’t have to worry about the battery acid sloshing around or spilling many ATVs take advantage of absorbed glass mat batteries. These batteries are generally lighter and can be installed at any angle.
• Premium Vehicles – Since these batteries cost about twice as much they are currently only being installed in premium vehicles such as the 5 Series from BMW. These batteries can help lower the overall weight of the vehicle while providing reliable power to the ever growing number of electronic component founds in a vehicle.
• Amateur Robotics – The power and durability of these batteries has made them popular in the world of amateur robotics. (You know, those cool fighting robots you always see on TV).
• Power Wheelchairs – AGM batteries are also used in power wheelchairs. Their overall power, safety and reliability make them a great choice for this application.