- by Bryan Veldboom - updated on 12/21/2021
What does "AGM battery" mean? Although they have been around since the 1980s, most people don't know what AGM stands for. The term AGM battery is short for Absorbed Glass Mat. AGM batteries have become increasingly popular in recent years. The wide use of AGM batteries is largely due to their unique design. The way in which they're constructed provides AGM batteries with a higher voltage output, which allows them to support the increasing amount of technology found in modern and heavy-duty vehicles.
Are you looking for the best battery for your car, truck, RV, golf cart, boat or powersport vehicle? An AGM battery may be the answer. Today, we'll be discussing how AGM batteries work, looking at the various features of AGM technology and what advantages AGM batteries have over traditional lead acid batteries. We'll also be talking about deep cycle AGM batteries and what to look for in an AGM battery charger.
Traditional flooded lead acid batteries are a fixture in vehicles such as cars, trucks, boats and RVs. Flooded batteries consist of a number of lead plates that are divided by a series of separators. These plates and separators are all packed inside a solid casing along with a liquid sulfuric acid called an electrolyte. For more in-depth information, read our blog entitled "How Does a Car Battery Work?"
AGM batteries are constructed a bit differently than flooded batteries. They still contain plates and an electrolyte, however, in an AGM battery, the plate separators are made of a special fiberglass material.
In a traditional flooded battery, the electrolyte is a free-flowing liquid, but an AGM battery absorbs the electrolyte in its separators and holds it there in suspension. It is the fiberglass material that helps enable AGM batteries to store the electrolyte in a dry state rather than in a liquid free form. This is what the term "absorbent glass" is referring to.
You might have heard AGM batteries referred to as Valve Regulated Lead Acid batteries or VRLA for short. AGM batteries are one kind of VRLA battery. The key thing about VRLA batteries is that they're constructed with a special valve that prevents gases from escaping the battery's casing.
So, why is that important? Lead acid batteries work by converting stored chemical energy into electrical energy. This is done through a series of chemical reactions that take place between the battery's plates and the electrolyte. During this process, the water in the electrolyte is split into hydrogen and oxygen gases. When that happens, it's possible for a flooded battery to lose some of its water due to evaporation. That's why flooded batteries require you to occasionally add distilled water to them in order to prevent them from becoming too acidic over time, which will shorten the battery's overall lifespan.
Because a VRLA battery is completely sealed, it prevents any gas from escaping, allowing it to recombine into water during the recharging process. This preserves the electrolyte's proper chemical concentration, giving the battery a longer life.
Due to their unique design, AGM batteries have a lower internal resistance than flooded batteries. This provides them with a number of advantages.
One of the unique things about AGM batteries is their ability to function as both SLI (Starting, Lighting & Ignition) and deep cycle batteries. SLI batteries are the type of battery that's used to start the engine in your car, truck or RV. They're built to provide short intense bursts of energy. Deep cycle batteries are engineered to provide smaller, more reliable amounts of power over a longer period of time. You can commonly find deep cycle batteries in applications like golf carts and floor scrubbers. They're also commonly used as the house battery in RVs and boats.
It's common for owners of RVs and boats to have two different types of batteries on board, a starting/cranking (SLI) battery to start the engine and a deep cycle battery to power additional applications such as clocks, lights and appliances. Due to their higher voltage output, AGM batteries can serve as dual purpose batteries that do a bit of both. AGM batteries have the strong starting power you need to start your engine, along with enough cycling power to run additional applications. Because of this, many RV and boat owners rely on a single dual purpose battery instead of having both a starting/cranking (SLI) and deep cycle battery on board. Want to learn more about RV and boat batteries? Read our blog articles entitled "Starting, Deep Cycle & Dual Purpose: Breaking Down Your RV Battery Options" and "Which Brand of Battery is Best for Your Boat?"
One important thing to keep in mind is that you can't charge an AGM battery using a standard battery charger. This is because AGM batteries have different charging requirements than standard flooded batteries. AGM batteries require a slower, more stable charge than flooded batteries and can't sustain the high charging speeds used by standard battery chargers.
If you charge an AGM battery with the wrong type of charger, you will end up under or overcharging your battery. Undercharging can cause sulfation on the battery's plates, reducing its ability to accept a full charge. Overcharging cooks the components inside the battery, which can shorten its lifespan or kill the battery entirely.
When shopping for battery chargers, be sure the model you select is compatible with the chemistry and voltage of the battery you'll be using it on. For instance, if you have a 12 volt AGM marine battery, you need a charger that works with 12 volt AGM batteries. Many modern chargers come with settings for a number of different battery types.
Batteries Plus can help you find the right AGM battery for a wide range of vehicles. Shop our selection of batteries for boats, RVs, golf carts, powersport vehicles, as well as cars and trucks. Are you looking for the best battery available for your car, truck or boat? Read about our exclusive X2Power AGM battery, one of the highest performing AGM batteries on the market. Having trouble finding a battery for your golf cart? Our blog titled "Understanding Golf Cart Battery Basics" can help.