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AGM - Absorbed Glass Mat Battery Technology


Absorbed Glass Mat Batteries

What is AGM, and what makes AGM technology better?

Absorbed Glass Mat batteries are constructed differently than the traditional flooded battery. This write up covers mainly the Concorde Sun-Xtender AGM's, but also applies to most other brands of deep cycle AGM batteries.

In AGM batteries (also called starved electrolyte), there is a thin ultra-fine fiberglass mat sandwiched between the plates that are saturated with battery acid to about 95% of what they can hold. This mat is then packed in between the plates and slightly compressed, then welded/soldered in place. Because the plates and mats are packed fairly tight, they are almost immune to vibration.

AGM (Absorbed Glass Mat) sealed battery technology was originally invented in 1980, and developed and introduced in 1985 for military aircraft where power, weight, safety, and reliability were paramount considerations. The Concorde AGM batteries a VRSLAB (Valve Regulated Sealed Lead-Acid Battery). Sometimes referred to as VRLA (Valve Regulated Lead-Acid). Several manufacturers now produce AGM batteries, but Concorde was the first to develop the technology for commercial non-military use.

AGM - Deep Cycle Or Not?

An important thing about AGM - Just because a battery is AGM does NOT make it a deep cycle battery. Several companies, such as Optima, have adopted AGM for starting batteries and other non-deep cycle applications. Those still have the advantages of AGM, but are not deep cycle. It is primarily plate thickness that makes a battery deep cycle, not whether it is flooded, gelled, or AGM.

The Concorde SunXtender batteries are essentially the same construction as the Concorde Lifeline, Chairman, and other Concorde AGM batteries. The major difference is that the Sun-Extender batteries have bolt-on terminals instead of the common post type. We feel that bolt on terminals give a much more reliable connection. We also stock many of the Concorde "Chairman" (designed mainly for wheelchairs) batteries and some "LifeLine" (marine & RV) batteries.

Battery Efficiency:

This comparison is important, and is critical for high charge or discharge rate applications. Internal resistance of a battery denotes its overall charge/discharge efficiency, its ability to deliver high currents without significant drops in voltage, and is a measure of the quality of the components and construction.

Battery Internal Resistance Losses:

Losses from internal resistance shows up as heat, which is why batteries tend to get warm when heavily charged or discharged for a while.

Internal resistance losses in standard flooded Lead-Acid batteries is usually around 10% to 15% for a new battery, and can be as high as 25%+ for older batteries. This can vary considerably, depending mainly on the age and quality of the battery. In general you get what you pay for - cheaper batteries with thinner plates and internal connections tend to be less efficient.

Gel batteries are better at approximately 12% to 16% internal resistance so would require around 115 amp-hours of charge for every 100 amp-hours used.

Concorde AGM has the lowest internal resistance of any commercial battery that we know of - only 2 percent in a new battery. In solar electric systems, this is the same as getting an extra 10 to 15% out of your panels. This also allows Concorde AGM batteries to be charged much faster if needed and also to deliver higher currents when required. Owners using high output alternators, operating inverter banks, or relying on solar panels can benefit significantly when using Concorde Advanced AGM batteries with their equipment. Concorde AGM's are more efficient.

Heat: Better efficiency means much less heat is developed in the batteries - any current that does not actually go to charging a battery turns into heat. That is why some batteries, especially older flooded batteries (and even some non-deep cycle AGM), can get very warm or even hot. In extreme cases you can get " thermal runaway", which can be dangerous. If you have ever felt the side of a battery under heavy charge, you have probably seen that they can get very warm.

Concorde batteries far exceed the US Coast Guard test for thermal runaway: These MW-SPEC (Military Specification) tests involve fully charging a battery, heating it to over 130 degrees (Potential Thermal Runaway Conditions) and then overcharging the battery to simulate a shorted cell. (16V for a 12V battery).

AGM Batteries Are Not Gelled Batteries:

Concorde AGM batteries are NOT a gelled electrolyte. It is considered a "Recombinant Gas Absorbed Electrolyte" battery. This cuts water loss by up to 98%. Loss of charge due to self-discharge is 3 to 10 times better than with conventional gelled, and 5 to 50 times less than with flooded batteries. The gasses recombine almost 100% within the battery, reducing Hydrogen emissions to a level far below most battery types, and less than half the lower explosive limit for Hydrogen. In addition, they do not have the charge and discharge current limitations that most gelled batteries have.

Concorde AGM battery technology has continued to develop and offer improvements over other sealed battery technologies. AGM technology has become the next step in the evolution of both starting and deep cycle sealed batteries for marine, RV, and aviation applications. These are the same batteries that the US Military uses in many of it's armored and standard vehicles. This "next generation" technology delivers increased safety, performance, and service life over all other existing sealed battery types, including gel technology. All Concorde AGM batteries carry a one-year full warranty - most gelled cells carry only a 90-day warranty.

AGM batteries have much better resistance to vibration and shock due to their construction than most flooded batteries. The plates are packed in with the glass mat, reducing plate movement and vibration to nearly zero. In addition, because the glass mats are not totally saturated and the liquid does not expand to cause plate and case damage, AGM batteries can withstand freezing - you will get little or no output from a frozen battery, but at least it will not ruin the battery or break the case.

Concorde AGM batteries meet MIL-SPEC B8565J and FAR 23.1353, 25.1353(c), 27.1353, 29.1353(3), 25.853(a). All Concorde AGM batteries are shippable without restriction by any means of transportation, including air. Hazardous labeling is not required.

In AGM sealed batteries, the acid is absorbed between the plates and immobilized by a very fine fiberglass mat. No silica gel, as is used in gelled, is necessary. This glass mat absorbs and immobilizes the acid while still keeping the acid available to the plates. This allows a fast reaction between acid and plate material. Even if the battery is broken, no electrolyte will be spilled.

The AGM battery has an extremely low internal electrical resistance. This, combined with faster acid migration, allows the Concorde AGM batteries to deliver and absorb higher rates of amperage than any other sealed batteries during discharging and charging. In addition, AGM technology batteries can be charged at normal flooded lead-acid regulated charging voltages, therefore, it is not necessary to recalibrate charging systems or purchase special chargers. Concorde AGM batteries can be bulk charged at high rates without damage - up to 10 times as fast as most gelled cells, and 4 times as fast as flooded batteries.

AGM batteries are not the best choice for all applications - they are rather expensive compared to flooded batteries. However, their safety and design features make them the battery of choice for many applications, such as:

  • Where you cannot have fumes or hydrogen, such as in poorly ventilated areas, or where fumes may cause corrosion to electronics, such as repeater and cell phone sites.


  • Where resistance to shock and vibration is important.


  • Where spilled acid from leaking, tipped, or broken batteries cannot be tolerated.


  • When installed in a location where maintenance would be difficult or expensive, such as remote communications sites.


  • Where the batteries may be subject to freezing (-40 degrees F or lower).


  • Anyplace where you need a reliable totally sealed battery for safety or environmental reasons - wheelchairs, medical standby power, inside RV's,                  computer room UPS systems, or in enclosed spaces in boats.