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3 Best AGM Batteries (Review and Buying Guide)

Compared to the traditional lead-acid battery, an AGM battery has a lot of advantages. Their low self-discharge rate means they hold a charge better between uses. Since they’re sealed, they don’t require filling or maintenance and won’t spill or leak. Thanks to that, they’re both more convenient and safer to use. 

Upgrading from a lead-acid to an AGM battery is an especially smart choice if you live in a cold climate. These batteries deliver more current and recover better from deep discharges so you can count on them to start your car, no matter the weather.

We’ve picked out our three top AGM batteries on the market in 2020 and compared them side by side below. If you’re thinking about getting a new battery for your car or truck, read on to find out which one is the best fit for your vehicle and budget!

Overview of the Top AGM Battery

 Optima Batteries 8004-003
Optima Batteries 8004-003 34/78 RedTop Starting Battery
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Optima Batteries OPT8020-164
Optima Batteries OPT8020-164 35 RedTop Starting Battery
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Odyssey 35-PC1400T
Odyssey 35-PC1400T Automotive and LTV Battery
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priceOptima Batteries 8004-003 Batteries OPT8020-164Odyssey 35-PC1400T
Dimensions10 x 6.9 x 7.8 inches
9.3 x 6.8 x 7.6 inches
13.5 x 11 x 9.8 inches
Weight38.8 pounds
31.7 pounds
50 pounds
CCA800720850
Reserve Capacity100 minutes90 minutes130 minutes
Volts12V12V12V
Lifespan (AVG/ Not Official)2 years (much more with good care)Lasts about 1-2 years (longer with good care)About 3-10 year

Buying Guide

Before you can decide if a battery is right for you, you need to understand what a battery does and which specs are the most important for its performance. 

If you’re already a battery expert, you can skip down to the full reviews below. For the rest of us, though, a quick rundown of what separates a great AGM battery from the pack will help you figure out exactly what to look for. 

What Is an AGM Battery?

AGM stands for “absorbent glass mat” and is a descriptive name, telling you how the power is stored and released inside the battery.

In a traditional lead-acid or SLA battery, potential energy is stored in metal plates inside the battery’s cells. These plates are submerged in an electrolyte solution, typically battery acid. When current passes through them, the acid reacts with the plates, releasing stored energy and converting it to power for your engine. 

The same basic concept applies to AGM batteries, as well. They still use metal plates which react with an electrolyte solution. Instead of liquid acid, though, the solution is a gel. This gel soaks into fiberglass mats that separate the plates. 

Lead-Acid vs AGM: What To Expect out of the Battery

You know now how the science of an AGM battery differs from other designs, but what does that mean for you as the user? Let’s take a look at some of the key advantages of AGM batteries. 

Maintenance

Traditional lead-acid batteries need to be periodically filled with water to maintain the electrolyte solution. This is because the water in the liquid evaporates through time and use. If it’s not replenished periodically, the battery will no longer function. 

Since they use a gel solution absorbed into mats, AGM batteries don’t require any filling or mechanical maintenance. As long as you keep them charged, they’ll be good to go when you need them. 

Longevity

The glass mats in an AGM battery also help protect the plates from taking as much damage when they release energy. This allows AGM batteries to maintain their maximum capacity for longer and gives them a longer overall lifespan. 

Durability

An AGM battery can better withstand harsh conditions than traditional lead-acid batteries. They’re more resistant to damage from vibrations and less susceptible to influence from extreme heat or cold. This is especially important for off-roaders who those who live in wintry climates. 

Safety

Battery acid is highly corrosive. Since lead-acid batteries need openings for refilling, this makes them prone to leaking or spilling. 

AGM batteries are fully sealed. They won’t leak unless dropped or punctured, and that makes them safer to use and store. 

Flexibility

Not every vehicle allows for batteries to be installed upright. A sealed AGM battery can be safely used even when it’s on its side. This makes it more flexible and useful for a wider range of applications. 

What Is the Purpose of an AGM Battery?

The main function of a battery in a vehicle is to provide a quick burst of current to start the engine. You may also hear these batteries referred to as “starting batteries” because of that primary purpose. 

In modern vehicles, the battery is also responsible for providing power to electronic components. AGM batteries generally have a higher reserve capacity than other lead-acid batteries of a similar size. This makes them better at providing high electrical loads even after starting. 

If your only electronics are things like window controls and lights, any car battery should provide enough power. For drivers with lots of after-market electronics, like a sound system or radar detector, an AGM battery is the better choice. You’ll keep all the electronics running without draining too much power to start your car. 

CCA and Reserve Capacity: Do You Need the Best Performance?

CCA stands for “cold cranking amps”. It differs from the CA (or cranking amps) in that it measures how much power the battery can produce at temperatures below freezing.

Temperature has a big impact on the efficiency of a battery. Hot weather makes a battery run better and release more energy. Cold weather has the opposite effect, reducing the battery’s overall power output. This is why a battery’s CA will always be higher than its CCA. 

Most car engines need about 600-800 amps to start. Larger vehicles like SUVs may need as much as 1,000 amps to get going, while commercial vehicles can take 1,500 amps or more. If you’re not sure how much power your engine needs to start, a quick search of your repair manual should provide the answer. 

If you live somewhere that gets snow in the winter, you’ll want to get a battery with a CCA rating that matches or exceeds the power needs of your engine. Those who live in regions where it’s warm year-round can instead use the CA rating to find a suitable battery. 

Where the CA and CCA measure a battery’s starting power, the reserve capacity is an indication how long it can provide continuous power. In a vehicle, this is mostly a measure of how well it will run electronics when the engine isn’t running. 

Most vehicle owners won’t need a reserve capacity higher than about 60 minutes. This is plenty to prevent the battery from dying if you accidentally leave the lights on while you run into the store, for example. 

Those with more extensive electronics may want to go a bit higher. A reserve capacity of 100-120 minutes is ideal to power full after-market sound systems or other high-use electronics. 

How To Care For an AGM Battery

You’ll often hear AGM batteries described as “maintenance-free” because they don’t need to be refilled. While they don’t require any specific maintenance routines, though, there are some best practices for using AGM batteries that will help them power your engine longer. 

Here are some top tips that will help you keep your AGM battery in optimal condition:

  • Store it in a cool, dry place, out of direct sunlight. Batteries maintain their charge and best when stored at a temperature of around 50°F. Make sure the area is well-ventilated, as well, since the battery will periodically discharge gasses while it’s stored. 
  • Keep the battery fully charged, especially when it’s in storage. You can attach it to a trickle charger to maintain the charge full-time, or check the charge about once a month and top it off as needed. When it sits for a long time, this accelerates a process inside the battery known as sulfation. This is when lead sulfate formed during the release of energy doesn’t return to the plates during charging. Over time, this reduces the battery’s capacity and performance. While it can be reversed with a battery maintainer, the best option is to prevent it from happening in the first place. 
  • Don’t overcharge the battery. Overcharging can permanently damage the cells, reducing the maximum capacity and lifespan. A smart charger can be a good way to keep the battery charged without overcharging, since it will only send a charge when the battery needs it.
  • When installing the battery, first apply about a tablespoon of petroleum jelly to each of the posts. This serves two purposes. First, it makes it easier to attach the cables securely. Second, it prevents corrosion on the terminals. This is an especially good step to take if you lived in a humid climate. 

Product Reviews

Optima Batteries 8004-003 34/78 RedTop Starting Battery

Optima Batteries 8004-003 34/78
Optima Batteries 8004-003 34/78 RedTop Starting Battery
3.93.9 / 5
The Optima 34/78 RedTop is the ideal starting battery for heavy use, with high power and good starting ability. It holds its charge well in storage, too, so it’s a good choice for occasional use.

Here’s an Optima AGM that seemingly does it all! Packing high CCA, respectable reserve capacity, and plenty of durability, it’s ideal for most cars out there.

At a Glance

  • 12-volt
  • 800 CCA
  • 10” x 6 78” x 7 1316”
  • 38.8 lbs
  • Vibration resistant
  • Maintenance-free
  • 100 min reserve capacity
  • The lifespan of about 2 years (more with good care)
Best Optima Batteries 8004-003 34/78 RedTop Starting Battery
Ideal for trucks, streetcars, SUVs, hot rods, and any other application.

Take a look at the specs above, and you’ll find this battery works great for most situations. But what those specs don’t show is how durable this battery is. We took it to the track and found it handled hard launches like a pro. No spills or dents in sight! Likewise, it’ll handle your off-roading needs just fine as well!

Something else that’s interesting to note here is that this battery is super easy to install. We tried three different cars, and each time it took a matter of seconds. So even if you’ve never replaced a gasket, you’ll fit this AGM in your car with ease!

One final note about this battery is that it’s perfect for your nicest show cars. During our tests, we found this battery could last months at a time without needing a trickle charge. So it’s great for that Challenger you only take out on the sunny weekends.

Pros

  • Great for non-daily use
  • Strong reserve capacity
  • Easy to install
  • Durable
  • Leak-proof and spill-proof
  • High CCA for sure starts in cold weather

Cons

  • Lifespan is on the shorter side
  • Terminals awkwardly positioned for some vehicles

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Optima Batteries OPT8020-164 35 RedTop Starting Battery

Optima Batteries OPT8020-164
Optima Batteries OPT8020-164 35 RedTop Starting Battery
3.83.8 / 5
The compact Optima 35 RedTop has one of the best power to size ratios you’ll find in an AGM battery, and will fit into more vehicles than larger batteries. 

Here’s a battery that proves great things come in small packages. The Optima 35 RedTop’s compact size allows it to fit easily in most cars. But don’t let its size fool you. This battery also packs plenty of cranking power when it needs to!

At a Glance

  • 12-volt
  • 720 CCA
  • 9.38” x 7.69” x 6.75”
  • 31.7 lbs
  • 90-minute reserve capacity
  • Lasts about 1-2 years (longer with good care)
Optima Batteries OPT8020-164 35 RedTop Starting Battery
The Optima Batteries OPT8020-164 battery, which is built for every road use, can work well at the ultra-low temperature.

Looking at this AGM’s size, you’ll notice it’s smaller than most other batteries on the market. So it’ll easily fit in a handful of cars. You’ll even get an adapter for easy height adjustments as well. This piece alone allowed us to snugly fit this battery inside a ’93 Mazda RX-7 with ease.

We also noticed that this battery felt like it offered more cranking amps compared to other batteries we’ve tested. It did an epic job of starting up our cars and keeping them going. So it’s definitely great even if you don’t live in a cold climate area!

Lastly, this AGM is without a doubt spill-proof, even more so than other AGMs. While not our most prideful moment, we hit our fair share of curbs and even a tire while testing. And each time, we noticed the battery never leaked or spilled. Even on a hot summer day, this battery never even made a trace of a mess!

Pros

  • Easy to recharge
  • Spill-proof in all mounting positions
  • Compact size
  • Good cranking power
  • Fits easily in most vehicles

Cons

  • Short maximum lifespan
  • Lower CCAs than other AGM batteries

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Odyssey 35-PC1400T Automotive and LTV Battery

Odyssey 35-PC1400T
Odyssey 35-PC1400T Battery
4.44.4 / 5
The Odyssey 35-PC1400T has excellent cranking amps in any weather, along with a high reserve capacity and a long maximum lifespan. This is the ideal choice in vehicles that use lots of after-market electronics


Now here’s a battery that’s packing the power! Even by AGM standards, the CCA and reserve capacity are simply ridiculous here. And that’s a good thing!

At a Glance

  • 12-volt
  • 13.5” x 11” x 9.8”
  • 50 lbs
  • 850 CCA
  • 130-minute reserve capacity
  • about 3-10 year lifespan
Cheap Odyssey 35-PC1400T
Providing twice as much power as a conventional battery.

Just look at those specs and you’ll find a freakish amount of CCA and reserve capacity here. Seriously, our car started instantly on a Colorado winter evening with no issues throughout the drive. So it’s a safe bet that it’ll do the same wherever you drive.

Also, this battery works great in cars with tons of after-market electronics. We tried it with a 3-amp bass system and noticed no light flickering. In fact, there were no electrical problems of any type. This becomes all the better when you factor in that high reserve capacity! Hence there’s plenty of room for fun here.Shortcode

And lastly, you’ll get a reliably long lifespan with this battery. Take good care of it, and it’ll last every bit of 3 years and plenty more! So it’s definitely one of the longer lifespans compared to other AGMs.

Pros

  • High CCA
  • Long lifespan
  • High reserve capacity 
  • Great for after-market electronics
  • Good cranking power

Cons

  • Needs more time and amps to recharge
  • Heavy and bulky

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The Bottom Line

Considering factors like durability, value, and capacity, we’d have to say our top choice is the Optima 34/78 RedTop. It strikes a great balance between power and weight, and has the CCA you need to start an engine in cold weather.

That said, there’s something to love about all three of these AGM batteries—that’s why we’ve singled them out and reviewed them here! Like we said in the buying guide, it all comes down to deciding which one is right for your vehicle’s needs. 

Whether you’re an off-roader or just need to get to work on time, any one of these batteries is a great choice for reliably starting your vehicle. We hope this information has helped you pick the right one for your car or truck!

FAQs

Can an AGM battery be a direct replacement for other chemistries?

That depends on the chemistry. Most vehicles with combustion engines use lead-acid batteries, which are similar to AGM batteries in size and performance. Many hybrid and electric vehicles use lithium-ion batteries, however. These cannot be replaced by an AGM battery. It probably won’t fit, first of all, and even if it does it won’t power the car correctly.  

In most cases, you can replace a lead-acid battery in a vehicle with an AGM battery without any issues. Some vehicles may require you to re-set the battery sensor system to note the change in chemistries. You may be able to do this yourself if you have the right automotive scan tool. If you don’t, any auto repair shop can do it for you. 

 Resetting the battery sensor is an important step. AGM batteries charge at a different rate than other lead-acid designs. If you don’t re-set the vehicle’s ECU to note the change, you could end up overcharging your battery while you drive. 

Do you need special batteries for off-roading?

Yes, and an AGM battery is exactly what you’re looking for. The battery in an off-roading vehicle has to be able to resist vibration and be durable enough to survive bumps and jolts. The spill-proof, rugged design of an AGM battery is ideal in this environment. 

Will any AGM battery fit my car?

No. Not all 12-volt batteries are the same size and shape. Instead, there are multiple group sizes that are used to differentiate batteries of different sizes. GMs and Chryslers, for example, often use group 34/78 batteries, while Subarus and Nissans use group 35 batteries.  

You’ll find the right group size for your vehicle listed in your repair manual. Alternatively, you can check the label of the battery that’s currently installed. 

Can I use my usual charger to recharge an AGM battery?

That depends on what kind of charger you use. AGM batteries do best when they’re charged slowly at a low rate of power, and are more prone to damage from overcharging than other lead-acid designs. 

Trickle chargers are ideal for AGM batteries since the low current they use is unlikely to cause damage to the cells. Smart chargers are a great choice, too. These chargers collect information from the battery cells during charging and adjusts accordingly. Many even have a designated AGM battery setting that will give you the ideal charge for the chemistry. 

How do I check the charge of an AGM battery?

The internal resistance of an AGM battery is lower than that of a flooded lead-acid battery. If you have an older battery tester, it might not be able to take an accurate reading.

Modern load testers have settings specifically for AGM battery that adjust to this low resistance. You can find these tools at any automotive repair store if you don’t have one on-hand. 

Once you have the right tool, simply turn it on and connect the tester’s sensor wire to the positive terminal of your battery. Connect the sensor’s black wire to the negative terminal, then read the display. 

When fully-charged, an AGM battery should read around 13 volts. If you see a reading of 10 volts or lower, it’s time to recharge your battery. 

How do I know when it’s time to replace my battery?

Using a load tester or multimeter to check the charge is the most reliable way. Follow the steps outlined above to get a voltage reading on the battery. If it’s 10 volts or lower, put your battery on a charger until it reads fully charged. Remove the battery from the charger and let it sit overnight.

In the morning, test the battery again. A few hours shouldn’t be long enough for a healthy battery to lose its charge, so it should still read full. If it’s dropped by more than 1 volt, the battery is no longer holding a proper charge and should be replaced. 

There are also signs you might notice while driving that your battery is on its way out. One common sign is that the headlights or interior lights flicker or are dimmer than usual. You may also find your car needs a few tries before it will start, or that electronics like the window controls are slow to respond (or won’t respond at all).

Keep in mind there are other things besides a dying battery that can cause these symptoms. Problems with the starter or alternator can also lead to power loss or difficult starts. Before replacing the battery, have it tested to make sure it’s the problem.

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