Enter the absorbed glass-mat (AGM) battery. AGM batteries are car batteries designed to deliver a lot of amps even when the engine is off. AGM batteries are also quickly becoming one of the most common batteries on the road.

The fiberglass mats spread more of the electrolyte in contact with the ultra-thin lead plates — all while cushioning the battery against knocks, bumps and vibrations. Because of the absorbent glass mats, battery makers can literally squeeze in more lead plates. More lead in the battery means more available power.

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How might tomorrow’s tech look in these cars? Auto-buckling seatbelts. DNA-coded locks. Touch screen windows. Engine parts using super-materials to avoid breaking or ever needing to be replaced. Maybe a flying-mode, too. The possibilities are endless.

Backup cameras, Bluetooth connections and other electronics will drain deep cycle AGM batteries in a way standard car batteries can’t handle. Standard lead-acid batteries used to fit the bill for cars because they can throw a lot of electricity into a starter in a short powerful burst. Then they need to recharge to 100% or else they start to die.

AGM batteries were originally developed in the 1970s for telephone boxes and computer rooms (yes, back when a computer took an entire room.) Their sealed design makes them nonspillable, making them ideal for onboard power in fighter planes, submarines and motorcycles. AGM batteries are the best car battery for vehicles with auto start stop engines because they can deliver deep power and still start a car engine.

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However, an AGM battery’s fiberglass mesh keeps that water trapped because it’s packed so tightly to the lead plates. On top of that, the sealed design holds the water vapor in, and only if you overcharge it will a molecules of water vapor escape.

Normally, when a standard battery recharges, electricity splits the water in the electrolyte into hydrogen and oxygen, which mostly gets absorbed back into the electrolyte. The rest of the hydrogen and oxygen escapes through vents in the case, and the battery loses water. Water loss can kill a car battery, and that’s why you should occasionally refill your standard batteries with distilled water.

Fiberglass mesh mats soaked in electrolyte carry current faster than liquid electrolyte. Yes, that’s how AGM batteries can deliver big bursts of power even if they’re drained. It’s also how AGM batteries recharge faster than regular batteries. That low internal resistance means AGM batteries can give more amps and accept more amps when they recharge.

The battery’s fundamental chemistry is still based on lead, sulfuric acid and water. When you draw power, the acid molecules move to the lead plates, leaving water and lead sulfate — and sending an electrical charge out of the positive post. Removing the sulfuric acid from the solution creates a chemical reaction between the paste on the plates. Recharging a battery works in reverse: Electricity goes in, making the liquid more acidic.

Also, every time the engine cuts off, the AGM battery steps in to run your air conditioning, fuel sensor, transmission, radio and all the other electronics that keep your car running smoothly.

What you might not expect is how the AGM battery’s fiberglass mats and special valve also protect its performance in extreme weather.

More than half of new vehicles sold after 2019 require an AGM battery because of their electrical power needs. As of 2022, more than 50 million vehicles on the road require an AGM battery.

Generally, an AGM battery can start your engine more than 60,000 times. That’s more than three times the starts you’ll get out of a standard battery.

If your car has an auto start stop engine, you might have an AGM battery. The most common vehicles with an AGM battery are recent model years of these cars:

Cold suppresses a car battery’s performance, forcing a car battery to work twice as hard to generate cranking amps. Because the fiberglass mats are tightly packed on the lead plates, an AGM battery can generate a lot of amps without facing a lot of resistance. Even if the cold slows down chemical reactions, an AGM has amps to spare.

That’s why boat and RV owners use an AGM battery. It may be several hours before you get back to the dock, or tonight’s campground might not have a shore power hookup.

The fiberglass mesh on the lead plates gives the electrical current a shorter, easier path to follow than in a regular battery with free-flowing liquid.

RVs and boats tend to use two types of batteries: one for starting engines and motors and one to power their electronics. AGMs can do both. RVs and boats need power for fish finders, food storage, cooking equipment, sound and entertainment systems and more. Instead of carrying two batteries, one for starting and one for deep cycling, owners of RVs and boats sometimes turn to a deep cycle AGM battery that can also start motors.

With a normal engine, you might start your car three or four times a day, assuming you drive to work and get a few errands done afterward.

AGM batteries are a kind of valve-regulated, lead-acid (VRLA) battery, which is part of why AGM batteries last so long. VRLA batteries have a one-way valve regulating how much hydrogen and oxygen can escape when the battery recharges.

However, there’s always a chance some water loss can happen when electricity splits H2O into hydrogen and oxygen gases. Losing those water molecules means the electrolyte stays more acidic than usual — cutting into the potential strength of the chemical reaction on the plates, and ultimately shortening the lifespan. The AGM’s valve stops those gases from leaving.

You don’t have to maintain VRLA batteries the same way. Their one-way valves keep the gases in the battery, effectively preventing water loss.

If you also find yourself replacing batteries more often than 3-5 years, you may want to upgrade to an AGM battery. Be sure to consult with an automotive professional first.

That’s called low internal resistance, and that’s how an AGM battery’s design that expand what car batteries can fundamentally do.

An auto start stop car might need three or four starts on one morning drive, depending on how many traffic lights you hit. No matter how well you keep it charged, a regular car battery cannot keep up with an auto start stop engine.

Specifically, the fiberglass mesh mats. They are the GM in AGM batteries. Ultra-thin glass fibers soak up all the electrolyte (water and sulfuric acid) into thin pillows cushioning the lead plates. Instead of the free-flowing liquid inside of a regular car battery, an AGM battery carries its electrical charge in soaked sponges — and those mesh sponges are coating the lead plates.

AGM batteries also have valves regulating the hydrogen and oxygen allowed to escape during charging. They fall under a broader category of valve-regulated, lead-acid (VRLA) batteries, also called maintenance free. If you’ve never thought much about maintaining your car battery, it might be thanks to this special one-way valve that essentially keeps evaporated water from leaving the battery case.

Safety, reliability, comfort always mattered to drivers. Technology and new inventions merely expand how engineers and car companies express these values. The more electronics on cars, the broader and faster the adoption of AGM batteries.

Plenty of drivers still use a car battery that follows the same fundamental design from when French physicist Gaston Planté invented the lead-acid battery in 1860. That’s changing. More than 10% of all the cars on American roads today rely on an AGM battery. In fact, more than half of all new cars sold between 2020 and 2022 require an AGM battery. That’s more than 27 million vehicles. Essentially, car buyers doubled the number of AGM-reliant cars in three years.

Draining a battery to 50% or so before recharging it is called deep cycling. Plain, flooded car batteries can’t deep cycle like AGM batteries. That’s why you might need to jump a car if you leave your headlights on for a couple hours with the engine off.

Standard batteries need more voltage than AGM batteries to recharge because regular batteries have higher internal resistance. To keep them from overheating, they can only take a few amps at a time at that high voltage.

That need is an incredible burden that a standard car battery can’t handle. They used to fit the bill for cars because they can throw a lot of electricity into a starter in a short burst. The design hasn’t changed much since the lead-acid battery was invented in 1859, except for small tweaks and a durable, plastic case to protect the lead plates and contain the sulfuric acid and water.

AGM batteries, on the other hand, can deliver a steady stream of amps and still give a big burst of power to start an engine. You can drain an AGM with all the electronics your car has and still expect it to crank the engine. The tight fiberglass mat design lets these batteries work well at partial discharge rates.

Heat weakens car batteries by evaporating the water out of them. The more fully charged a battery is, the more acidic its liquid, the harder it is for water to evaporate out of it.

The absorbed mats give AGM batteries a sponge-like resistance to vibrations. A regular car battery’s sensitive internal components can break apart if you shake it hard enough. Its lead plates are hanging from a sturdy metal in liquid. Even if you don’t break the plastic case, it’s common for car batteries to die if you rattle them hard enough.

This means AGM batteries need a special AGM charger. They can take a lot of amps in a short period of time — but an AGM battery charger must keep its voltage lower than 14 volts to avoid ruining the AGM battery. AGM batteries are 12 volts, like all car batteries, and can handle some higher voltage, but only up to a certain point. If a car alternator charges an AGM battery with a voltage higher than 15 volts, it can damage an AGM. It’s not likely, but voltage fluctuations are a possibility.

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If you use a standard battery charger for an AGM battery, the high-voltage current must pass through anything it can. That means breaking up more water molecules and building up too much gas inside. Too much gas trips the safety valve. That releases some gas, reducing pressure. However, if you keep charging it with high voltage, too much gas and pressure will pop that valve out or break the case’s seal.

AGM means absorbed glass mat, and it means the battery acid inside is absorbed into fiberglass mats instead of sitting as a free-flowing liquid.

Even a car without auto start stop can strain its car battery because of all the electronics onboard. With collision sensors, fuel sensors and air conditioning to run, an alternator has fewer amps to give your car battery. Unless you’re traveling at highway speeds, recharging your car battery isn’t a priority for your alternator. In that case, a regular car battery might go for a while between recharges, and that’s not good for it.

An AGM battery’s sealed, spillproof design allows them to pass the specific transportation regulations. You can ship them by air, deliver them by mail, etc. It might be odd to think of spilling a car battery, but you should understand that standard car batteries are not as durable as AA batteries. They’re more like a full cup of water with a sippy cup lid. If you turn it over, it spills or leaks. AGM batteries are more like sealed soda cans. You can transport them (gently, please), and they won’t spill.