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What is an AGM Battery?

Power - by Bryan Veldboom - updated on 1/5/2024

three X2Power AGM batteries

We talk about them all the time and they are some of the best batteries around. What the heck is an AGM battery anyway? They have been around since the 1980s and are becoming more and more popular among automotive manufacturers and enthusiasts. But many people don't know what AGM stands for or why they are becoming the preferred automotive battery choice.

What Does AGM Stand For?

The term "AGM" is short for Absorbed Glass Mat. AGM batteries are built a little differently than your conventional flooded car battery. How they're constructed provides AGM batteries with a higher voltage output, which allows them to support the increasing amount of technology found in modern, heavy-duty or high-performance vehicles.

What's the Difference Between an AGM and a Flooded Battery?

Traditional flooded lead acid batteries are a fixture in vehicles such as cars, trucks, boats and RVs. Flooded batteries consist of many lead plates that are divided by a series of separators. These plates and separators are all packed inside a solid casing and are filled with a liquid sulfuric acid called an electrolyte. When you shake a flooded battery you can actually hear liquid sloshing around inside. Don't go and shake your battery relentlessly, it could be bad for the battery if you shake it too much.

AGM batteries on the other hand are designed with durability and performance in mind. Instead of a free-flowing liquid electrolyte solution, AGM batteries use fiberglass mats that are soaked in the electrolyte and then tightly packed in between the plates. This is also where the term "absorbed glass" comes from.

Inside look at an agm battery

The tightly packed fiberglass separators provide more durability while also allowing more power production to give you the "oomph" you need to keep all of your electronics working. As an added benefit, these batteries are also almost completely maintenance-free.

For more in-depth information, read our helpful blog "How Does a Car Battery Work?"

How Do I Know if My Car Has an AGM Battery?

It's not like you can just crack open the battery to see what kind it is. That would be very dangerous and you would completely destroy your battery, so how do you know if you have one? Luckily, it's stated on the label. Also, if you don't have easy access to the battery to visually inspect, it will also be stated in the vehicle owner's manual.

Another thing to consider is the vehicle that it's in. If your car, truck or SUV has a lot of electronic features and uses stop/start technology, then there is a good chance that your vehicle is equipped with an AGM battery.

Are AGM Batteries the Same as Valve Regulated Lead Acid Batteries?

If you've been researching batteries you may have come across the term "valve-regulated lead acid" or VRLA. AGM batteries are just one type 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. All AGM batteries are valve-regulated but not all VRLA batteries are AGM. VRLA batteries are available in different lead-acid types, Wet-cell (flooded), Gel and AGM.

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 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, a flooded battery can lose some of its water due to evaporation. That's why traditional flooded batteries require you to occasionally add distilled water to them 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.

What are the Advantages of an AGM Battery?

Thanks to their unique design, AGM batteries are more durable and have a lower internal resistance than flooded batteries. This provides them with many advantages.

  • Higher voltage output - AGM batteries provide more electrical energy than flooded batteries, making it easier to start vehicle engines and providing additional power for additional electronics such as touchscreens, backup cameras and fuel-saving start-stop systems
  • Faster recharge rates - AGM batteries charge up to five times faster than conventional flooded batteries.
  • Longer lifespans - AGM batteries can last up to three times longer than flooded batteries. Their long lifespans can be cost-effective in the long run.
  • Slower discharge rates - An AGM battery holds its charge longer when it's not being used and is more likely to be recovered if it does become completely drained.
  • Spill-proof - AGM batteries are spill-proof because the electrolyte is held in place by the plate separators and the battery is completely sealed. This allows you to mount an AGM battery in a variety of positions that aren't possible with a flooded option.
  • Weather and temperature resistance - AGM batteries do a much better job of standing up to the negative impact of extreme cold and heat.
  • Vibration resistance - AGM batteries are much more resistant to vibration, making them ideal for boats, personal watercraft and off-road or high-performance vehicles.

Can AGM Batteries Be Used for Deep Cycle Applications?

One of the unique things about AGM batteries is their ability to function as both SLI (Starting, Lighting and 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 (and other things). They're built to provide short intense bursts of energy.

Deep-cycle batteries are designed and engineered to provide smaller, more reliable amounts of power over a longer period. 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.

Are AGM Batteries Good for RVs and Boats?

It's very 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 (or several) to power additional applications such as clocks, lights, trolling motors, fish finders and appliances.

Due to their higher 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?"

Can You Charge an AGM Battery with a Regular Charger?

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 several different battery types.

Shop AGM Batteries at Batteries Plus

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.

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