Automotive technology has advanced at ludicrous speed, yet modern automobiles still use battery technology that originated in the early 1900s. We should clarify we’re not referring to the battery packs in electric vehicles but the 12-volt battery under the hood of your gas-powered car. Nearly every vehicle you see on the road today uses a lead-acid battery to start the car and run basic electronics when the engine is off. So there has to be a better way, right?

Not exactly. The motorcycle industry is an interesting barometer as it’s enjoyed great success with lithium-ion batteries. Not only are these batteries much lighter than their lead-acid counterparts, but they also offer considerably more cranking power. So it sounds like everyone in the automotive industry would bite your arm off for one. Right? Not so, as these newer batteries experience a considerable performance drop in cold conditions and cost more than the “legacy” alternative.

The best solution in the interim is what’s called an Absorbed-Glass Mat Battery. It enjoys the reliability of a lead-acid battery while presenting impressive performance at a reasonable price.

How Do They Work?

Before we get any further, it would be slightly disingenuous to say lead-acid batteries haven’t changed at all during their life span. That simply isn’t true. The lead-acid chemistry is really all that’s remained from day one. Nearly everything else has changed with Absorbed Glass Mat (AGM) batteries taking the industry by storm. For a crash course on how car batteries work, check out this Youtube video.

Invented in 1859, lead-acid batteries are brilliantly simple and capable. Just as the name implies, they use lead plates submerged into diluted sulphuric acid to sustain a controlled chemical reaction, giving the negative terminal a negative charge and vice versa for the positive terminal. When not in use, the electrons on the negative terminal inherently want to flow back to the positive terminal. They can’t move through the sulfuric acid solution, but can move through a completed circuit that allows them to flow where they want to go—when positive and negative are connected to a device that needs power.

Along with adding a plastic case for protection (and battery acid containment) these batteries have experienced substantial improvements under the hood—no pun intended.

All car batteries use lead-acid chemistry, but there are two different schools of thought. The legacy batteries that we were talking about above are called wet-cell batteries. And they’ve worked just fine for decades. However, newer vehicles with complex electrical systems and tech require much higher electrical demands making Absorbed Glass Mat (AGM) batteries almost a necessity to keep them running properly.

Wet Cell Batteries

As mentioned above, conventional “wet cell” batteries use lead plates submerged into an electrolyte solution (battery acid) to sustain a controlled chemical reaction. Each battery has six cells, charged up to 2.1 volts each. While these have worked just fine for decades, Absorbed Glass Mat (AGM) technology is a much newer variation on the lead-acid theme.

AGM Batteries

Absorbed Glass Mat (AGM) batteries were originally developed in the 1960s to meet the high-performance demands of military aircraft. The move to replace the outdated Ni-Cad batteries was motivated by the need for superior performance, safety, and reliability that these military aircraft demanded—a list including fighter jets.

AGM batteries still function using the same principles as lead acid batteries. They use ultra-thin fiberglass mats to absorb battery acid instead of submerged lead plates—making them spill proof. However, the real genius with these thinner mats is they allow more battery acid to make contact with the lead plates. Thinner plates mean manufacturers can pack more of them in the same given space, making these batteries considerably more energy-dense than their wet-cell counterparts.

This technology showed up in the automotive world in much the same way it did with military aircraft thanks to the increased electrical demands of newer vehicles. In fact, most new vehicles actually need AGM batteries for standard equipment like stop-start, where the engine turns off when you come to a stop. That combined with the greater number of screens and onboard systems makes these more advanced batteries a necessity.

At the end of the day, the best thing that you can do is buy a like-for-like replacement for the battery that your vehicle came with.

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Lithium-Ion vs Lead Acid

Lithium-ion has often been included in the automotive battery conversation. However these batteries have never really come to fruition. The reason? They’re incredibly expensive, and not much better than the AGM batteries that we talked about above. For comparison sake, let’s say I’m hypothetically in the market for a new car battery. My Volkswagen GTI can accommodate an H5 or H6 group size battery.

Interstate Batteries’ premium AGM option can supply 950 cranking amps, weighs 45 pounds, and costs less than $300. A comparably-sized Antigravity battery can supply 1500 cranking amps, weighs 16.5 pounds, and costs just under $1000. Need we say more?

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The Good of AGM ✅

Deep Cycle Applications

Draining a battery to 50 percent before recharging it is referred to as deep cycling. This can often happen in the winter months when you leave your car or motorcycle dormant for extended periods of time; without the engine running, the alternator isn’t able to charge the battery back to full power. But, an AGM battery can be discharged much further than a wet-cell battery while sustaining similar levels of performance; think of it as the automotive grand-champion at Limbo.

Recyclable

Nearly all components used in AGM and wet-cell batteries can be processed and reused. Recycling centers sort batteries by type and chemistry before the solids are shredded and melted down. The byproducts can then be used to manufacture new batteries. However, the remaining liquids and other toxic substances must be appropriately disposed of. In fact, 99 percent of all lead acid batteries are recycled, according to the U.S. Environmental Protection Agency.

Durability

Initially designed for the aerospace industry, AGM batteries are over-engineered from the factory. Their biggest advantage is being spill-proof thanks to the fiberglass mats keeping the battery acid contained. This “sandwich” of mats and plates also adds structural integrity and vibration resistance, making these batteries a common choice for race cars and even marine applications.

The Bad of AGM ❌

Expense

As we talked about above, AGMs remain more expensive than a bog standard wet-cell battery. Having said that, they’re still considerably less expensive than a lithium-ion car battery. As time goes on, we reckon that AGMs will continue to become more affordable and could even replace wet-cell batteries altogether.

Overcharging Resistance

AGM batteries despite all of their advantages aren’t perfect. One of their major pitfalls is dealing with overcharging. Thankfully this doesn’t mean they’ll go bang under high voltage. Rather, it means their lifespan will be considerably shortened in those conditions.

Which Should You Choose?

At the end of the day, the best thing that you can do is buy a like-for-like replacement for the battery that your vehicle came with. Thankfully, manufacturers make it pretty easy to verify what type of battery you have. The label on an AGM battery will say “AGM” on it. You can also look up the model number on the manufacturer’s website.

AGM batteries will likely be the standard for the next couple of decades. Their superior durability and affordability make them the easy choice next to lithium-ion or wet-cell batteries. At the very least, you can tell your friends you have the same type of battery the Concorde used. If they can withstand the demands of supersonic flight, they’re most likely good enough to use in your car.