AGM Batteries Overview: What, Why, and Key Differences

What Is an AGM Battery?

AGM batteries are engineered for use in demanding conditions, such as extreme abuse, longer-than-average storage times, extreme weather, and frequent starts.

AGM stands for absorbent glass mat, which refers to the battery's internal structure. Instead of utilizing flooded lead plates, an AGM battery contains fiberglass mats that transfer the electrolyte solution between plates. This design offers several benefits compared to traditional flooded batteries.

How Do AGM Batteries Differ from Flooded Lead Acid?

Technically, an AGM battery is still a lead-acid battery. However, rather than containing flooded cells filled with an electrolyte solution, this solution is confined to absorbent fiberglass mats. This design makes AGM batteries essentially spill-proof, leak-free, and far more durable than traditional flooded batteries. AGM batteries also exhibit improved performance in high-demand applications.

AGM Battery Benefits

Aside from the factors we’ve already covered, AGM batteries offer numerous advantages over other dated technologies.

Durability

AGM batteries are far less susceptible to damage caused by vibration and shock when compared to lead acid. This quality is particularly useful for truck owners who spend time on uneven terrain such as mud, rocky trails, and other off-road destinations.

Resistance to Heat and Cold

Extreme temperatures wreak havoc on a traditional flooded lead acid battery’s lifespan. An AGM battery is much more resistant to loss of power and lifespan brought about by scalding heat and frigid cold, making it less likely to give up right when you need it most.

Variable Mounting Options

Lead acid batteries must be mounted with the posts facing up (or to the side-on-side terminal batteries) to prevent the electrolyte solution from leaking out of the case. Since the electrolyte is suspended in an AGM battery, the battery can be mounted on its side. This characteristic is useful in custom applications where space is limited.

Rapid Recharges

Conventional flooded lead acid batteries feature a high internal resistance, requiring slow, low-amperage current to charge effectively. By comparison, AGM batteries have a far lower internal resistance, allowing them to absorb current far more rapidly than conventional flooded lead acid. These differences lead to much shorter recharge times.

Longer Service Life

Typical AGM batteries can start a vehicle approximately 60,000 times before failure—that's nearly three times as many starts as conventional flooded lead acid batteries. This quality provides AGM batteries with a much longer service life—up to 10 years in ideal conditions. 

Enhanced Deep Cycle Capabilities

“Deep Cycling” refers to draining most of a battery’s power before recharging it. This term is commonly used to describe RV and overland auxiliary battery setups that see considerable use before recharging. AGM batteries offer far better deep cycle capabilities than conventional flooded lead acid, featuring a DoD (Depth of Discharge) of 80 percent versus a flooded lead acid’s 50 percent.

Power You Can Depend On

Because AGM batteries are less prone to damage and have reduced power, you can be confident that you’ll have the starting power you need for everything from hailstorms to heat waves.

Can You Replace an AGM Battery with a Lead Acid Battery?

A common question surrounding AGM batteries is whether or not replacing an AGM battery with a standard flooded lead acid battery is possible. To which we reply, “That depends.”

For us, the factor that determines a yes or no answer is whether or not the vehicle came from the factory with an AGM battery. If yes, then we’d recommend replacing the AGM with another equivalent AGM battery. In most cases, AGM batteries are installed from the factory in high-demand applications, like vehicles with considerable electronics or auto start/stop capabilities. In these applications, a standard flooded lead acid battery likely would not meet the required demands.

However, suppose your vehicle came from the factory with a flooded lead acid battery that was later upgraded to an AGM. In that case, you’re likely okay with replacing it with another flooded lead acid, so long as the vehicle isn’t equipped with a slew of high-demand aftermarket electronics.

Recharging an AGM Battery

While AGM batteries feature quicker recharge rates than flooded lead acid, you’ll need to follow a special procedure to ensure safe and efficient recharging and prolong the life of your battery. But first, let’s check out some tips from our experts.

Ten Amps or Less

If your AGM battery has been discharged beyond your alternator’s ability to maintain it, the battery should be recharged as soon as possible. When recharging, make sure the battery doesn’t exceed 10 amps at 13.8 to 15 volts during the recharging process. The process may take several hours, typically two to eight, but up to 12 hours on deeply discharged batteries.

If your battery charger has specific settings for AGM batteries, make sure you utilize them to optimize the recharging process. By keeping the charging amps at 10 or less, you’ll avoid overheating the battery and prolong the battery’s overall lifespan.

What Not To Do

Keep in mind that an AGM battery isn’t the same thing as a gel cell battery. An AGM battery has no free-floating electrolytes, while a gel cell suspends the electrolyte in a gel state. For this reason, you should not use the gel cell or spiral cell settings on your battery charger when recharging an AGM battery.

While batteries can be recharged more quickly by surpassing the recommended 10-amp limit, this will cause the battery to heat up, which can shorten its overall life. If your battery is registering 10.5 volts or less, a standard battery charger may not be able to return the battery to operating condition. A top-of-the-line charger may be required in this situation.

Step-by-Step Instructions

When recharging your vehicle’s AGM Battery, follow these steps.

Step 1: Purchase the Correct Charger

Purchasing the right charger is crucial when recharging an AGM battery. Select a charger designed exclusively for AGM batteries or one with AGM settings, ensuring the proper current flow.

Step 2: Connect the Charger

With the proper charger selected, connect it to the battery. This can be done with the battery removed from the vehicle or installed with a disconnected negative battery terminal. If choosing the latter, wrap the negative terminal in a cloth to prevent it from touching bare metal.

Step 3: Begin Charging

With the charger connected and set to the proper values (12V, AGM), begin charging the battery. Depending on the state of discharge, this may take anywhere from two to 12 hours.

Step 4: Monitor the Battery

While charging, monitor the battery for charging status and temperature. The battery's temperature should not exceed 40 degrees Celsius (104 Fahrenheit) to prevent overheating and overpressurizing.

Step 5: Reinstall/Reattach Terminals

Once the battery is fully charged, either reinstall the battery or reconnect the terminals. At this point, you should have successfully recharged your AGM battery. Test out the battery to verify its effectiveness.

Best AGM Batteries

With AGM benefits and recharging procedures covered, let’s discuss the top AGM batteries on RealTruck.

ODYSSEY Extreme Series Automotive Batteries

Offering outstanding quality, impressive specifications, and an industry-leading warranty, ODYSSEY Extreme Series Automotive Batteries top our list. This reliable, thoroughly proven battery features an up to 10-year service life, two-year storage capabilities, and ultra-fast recharging in under six hours. 

The ODYSSEY Extreme Series Automotive Battery accomplishes these impressive feats with its high-compression AGM plate separators and a heavy-duty case, offering unmatched durability in any condition—shock and vibration don’t stand a chance. 

ODYSSEY batteries come backed by a premium warranty—up to 4-years. 

Features:

• Service life of up to 10 years

• Can be stored for up to two years without recharging

• 100-percent recharge in less than six hours

• Resistant to vibration and extreme temperatures

• Maintenance-free Drycell design

• Up to 4-year full-replacement warranty

OPTIMA YELLOWTOP Automotive Batteries

OPTIMA is a leader in automotive battery innovation, renowned for its high-end, performance-oriented AGM batteries engineered to work as hard as your truck.

OPTIMA employs only the finest-quality materials and industry-leading technology, delivering up to three times longer service life and 15 times more vibration resistance than traditional flooded lead acid batteries. Due to the YELLOWTOP’s AGM design, this battery is virtually spill-proof. Mount it in any orientation, in any location, for reliable performance. The YELLOWTOP also excels in deep cycle applications, featuring lower CCA (cold cranking amps) but more reserve capacity. 

OPTIMA YELLOWTOP Automotive Batteries come backed by a 3-year warranty.

Features: 

• Offers deep-cycle performance and cranking power

• Up to three times longer life than traditional batteries

• 15 times more vibration-resistant

• AGM technology makes these batteries virtually spill-proof

• Mountable in virtually any position

• Maintenance-free

• Faster recharging with optimal starting power

• 300+ discharge/recharge cycles

• 3-year warranty

ODYSSEY Performance Series Automotive Batteries

While not as powerful as comparable batteries in ODYSSEY’s Extreme series, the company’s Performance Series Automotive Batteries deliver the same industry-leading quality, reliability, and impressive performance.

The Performance Series is ideal for those who don’t require the added CCA of the Extreme Series, but still desire unmatched reliability. Featuring the same build quality as the Extreme Series, including high-compression AGM plate separators and a heavy-duty case, the Performance Series is the perfect addition to any RV, daily driver, or mild wheeler.

ODYSSEY batteries come backed by a premium warranty—up to 4-years. 

Features:

• Service life of up to 10 years

• Can be stored for up to two years without recharging

• 100-percent recharge in less than six hours

• Resistant to vibration and extreme temperatures

• Maintenance-free Drycell design

• Up to 4-year full-replacement warranty

OPTIMA REDTOP Automotive Batteries

Get unmatched performance from your starting battery with OPTIMA REDTOP. These premium AGM batteries are engineered to provide quick, powerful bursts of energy, featuring higher CCA yet lower reserve capacities compared to the company’s other automotive offering—the YELLOWTOP.

Sporting OPTIMA’s SpiralCell AGM design with its Pureflow technology makes the REDTOP up to 15 times more durable against vibration damage compared to traditional flooded lead acid batteries. Whether mounted on a heavy-duty tow rig or rock-bouncing wheeler, the OPTIMA REDTOP delivers unmatched performance. 

OPTIMA REDTOP Automotive Batteries come backed by a 3-year warranty. 

Features: 

• Strongest 5-second starting burst

• Up to 3X longer life

• 15 times more vibration resistant than regular batteries

• Sealed design means little chance of leaks

• Mountable in virtually any position, even on it's side

• Faster recharging than traditional batteries

• 3-year warranty