We have written about the AGM battery on several previous occasions, first introducing it to our audience when very few new vehicles were equipped with them, then addressing some of the unique service aspects of the AGM battery versus the traditional flooded lead acid battery. In the time we have been writing this blog, the AGM battery has significantly increased in popularity, including in new vehicle installations, vehicle replacement battery applications and non-vehicle installations. In fact, the global market for AGM batteries exceeded $10B in 2020 and is expected to grow to nearly $15B by 2027 (marketstudyreport.com). So, understanding how to diagnose and service this versatile battery type is increasing important for technicians, repair shops, vehicle owners and anyone who has AGM batteries installed in their equipment

Why Has the AGM Battery Become So Popular?

Several market forces have combined to drive the growth of AGM battery usage, but in our opinion, the key aspect driving AGM growth is the ability of AGM batteries to better handle deep discharge applications and sustain their performance over time in these applications. This includes the usage of AGM batteries in the vast majority of vehicle Stop-Start applications in the North American carpark. Stop-Start operation results in deeper discharge of the vehicle’s battery(ies) – some systems use a multi-battery configuration – than does a traditional electrical system design. As a result, many OEs have chosen to install AGM batteries into their Stop-Start system configurations to withstand the stress caused by the repeated starting and periods of battery only system support during stops that are characteristic of the systems. In addition, the ability to handle deep discharge conditions makes the AGM battery great for a variety of other applications, such as marine, RV, powersport, racing and backup power applications.

What Makes the AGM Battery Different?

AGM contruction
Graphic courtesy of power-sonic.com

The term AGM stands for Absorbent Glass Mat. In an AGM battery, each lead plate is wrapped in fiberglass mat material, allowing the plates to be very thin and enabling more plates to be built into the battery, which results greater power (since a battery’s power is a function of its total plate surface). Then, when electrolyte is added to the battery it is absorbed by or suspended in this fiberglass mat material. This is very different than the free liquid found in a flooded lead acid battery. Also, the AGM battery is sealed and maintenance free, eliminating the ability to or need for adding water to it over time.

These differences in construction are what causes its characteristics to be different than a flooded lead acid battery. As we noted above, its construction allows an AGM battery to fully recover from deeper discharge situations, allowing it to be deployed in applications where a flooded battery would not survive. AGM batteries are also significantly more vibration resistant, allowing them to be used in applications where they will see rougher treatment. And, because they are sealed, they can be stored, charged and discharged in any position, allowing them to be installed into applications where a flooded battery would spill and damaged the equipment it is installed in. For instance, our handheld jump starters are used and stored in a variety of situations and conditions without issue, thanks to their internal AGM batteries.

What Do I Need to Know to Service AGM Batteries?

Since the AGM battery utilizes a completely different construction than a flooded battery, these changes have implications when it comes to servicing them, especially when it comes to charging and maintaining these batteries. Because they are completely sealed, AGM batteries are very sensitive to voltage (in a battery, voltage equals pressure). This means that care must be taken to not overcharge (raise the voltage too high on) an AGM battery. Most AGM batteries have a maximum voltage limitation from 14.4V to 14.65V at 70˚F.

The most important thing to keep in mind is that any charger or maintainer used on your AGM battery must be AGM compatible or AGM optimized. It is critical to confirm that any charging equipment is safe for use on an AGM battery (compatible) or specifically design for AGM service (optimized). All SOLAR PRO-LOGIX and CHARGE IT! battery chargers and maintainers are safe for use on AGM batteries and most models have specific charging routines available for optimal AGM charging (more below).

Beyond using a properly calibrated charging device, what else should you keep in mind when it comes to servicing these batteries? Here’s a quick checklist adapted and augmented from an article published over at practical-sailor.com:

    • Charged as often as possible. Lead acid batteries (of any kind) don’t like to sit in a discharged state for long.
    • When recharging, ensure that you get the battery back above 85% State of Charge before returning the battery or equipment to service.
    • Avoid discharging the battery beyond 50% State of Charge.
    • Use a temperature compensated charger (all PRO-LOGIX products have temperature compensation).
    • Charge at a rate no greater than 20% of the battery capacity being charged. So, for an 80AH battery, charge at 16A or less rate of charge. Low and slow is the way to go if long battery life is your primary objective.

When it Comes to AGM Charging – We’ve Got You Covered!

Our PRO-LOGIX series of battery chargers has many benefits for shops, technicians, fleet service facilities and consumers alike, but one key benefit is that PRO-LOGIX chargers properly charge a wide variety of lead acid battery types, including AGMs. That includes traditional AGMs, Spiral Wound batteries, Start-Stop AGMs and pure lead AGM batteries.

Whether you need a wheeled charger for high power charging in a busy service facility, a portable charger to support a wide variety of service applications or a battery maintainer to keep your “baby” ready for the spring thaw, AGM charging is built into the DNA of PRO-LOGIX chargers.

In addition, PRO-LOGIX delivers automatic operation, temperature compensation for exact charging accuracy, enhanced maintenance mode (most models) for optimal long term charging, reverse polarity protection, special Soft Start and Recondition modes to properly handle problem batteries, and the convenience of a forced start mode that allows the charger to activate when connected to a completely discharged battery. That’s why we they’re “Not Just Smart – Intelligent.”

What has your experience been like with AGM batteries? Any horror stories to share? Any service issues you’ve encountered? We’d love to hear about them in the comments below.

7 thoughts on “AGM Batteries – What You Need to Know”

  1. Have had a agm battery in my Mercedies for 17 years. Have replaced the battery 4 times.The only problem i have found is battery has discharged to 3.4 volts . this problem has occured with three of the batteries. However i have found rechargeing even with a AGM rated charger batteries will not fully charge. Each time this occures have had to remove battery and shake it.Then place it back on the AGM charger and it will take a full charge. And can be placed back in service for about a year.. expect
    battery is flaking inside and causing some kind of short. Ashaking battery seems to clear short. Eact time this has happened the battery voltage has dropped to 3.4 volts. Shaking battery is only way to get it to take a charge. thenbattery remains useable for about a year. overall have been happy with the AGM battery H groulp with 900 cca

    1. Richard – Thanks so much for sharing your experience. That’s amazing. 3.4V would be a good indicator of a short, for sure. I have never heard of shaking them to resolve the short. I bet this tip will help some of your fellow readers who have experienced something similar. Thanks again for letting everyone know. Jim from Clore Automotive

    2. I have 2 classic cars with AGM batteries. I have found the same issue as you, with the car that I rarely use, compared to one I use quite regularly. I was tired of lead-acid batteries lasting 1-2 years, so in 2006, I bought AGM batteries for both of them. Same brand, same model. The car I don’t really use seemed to get just 4-5 years from a new AGM, and I questioned the last replacement (July 2020) when the car I use more often is still on the same battery after 14 years. The battery supplier mentioned shaking the battery. After some discussion I then realised the lack of use was killing the battery. Sure, it was cycled – car started, run for 20-30 minutes, and usually taken for a short (1 mile) drive around the block. This would occur every 2-3 months or so. I would also put it on the trickle charger (AGM cycle) every month that I didn’t use it. But it seems the lack of movement is the issue with that car killing batteries. As it’s been a year since we worked this out, I plan to swap the batteries between the cars annually to try and prevent this. It makes me wonder if the same issue affected the lead-acid batteries that would barely last their warranty.

  2. AGM Batteries deliver voltage and except voltage better than tradition flooded lead acid batteries.
    However, AGM batteries when discharged “must be recharged” as soon as possible. If this is not done they will be unable to hold their true voltage of 12.8 and will settle after charge at approximately 12.3 volts. The damage has been done…
    At this voltage the AGM battery will load test good, but will direct your alternator to charge the battery, as the voltage remains at 12.3 when your cars system expects the battery to be 12.8 volts.
    With this voltage the alternator will be over worked and can cause premature alternator failure.
    *Key to Long Life: Always recharge after using or have an AGM maintainer connected to the battery when in storage.

    1. Dan – You make some great points. Agree that AGM batteries do not want to sit in a discharged condition. This is true for our lead acid jump starters as well, which contain AGM batteries. As we say, “charge early – charge often.” Thanks for adding to the discussion. Jim from Clore Automotive

  3. Jim, I would add that for seniors, parents and other drivers who drive less than five miles, AGM batteries make a great deal of sense. The reason is because they have a higher acceptance rate meaning that the battery will recharge faster than a conventual flooded battery on these short trips. An added advantage is that AGM batteries require very little maintenance and typically have longer free replacement warranties due to their reliability.

    1. Bill – Thanks, as always for adding to the discussion. Great points. Agree that these batteries make sense for those who use their vehicle infrequently. Thanks, Jim from Clore Automotive

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