Your Corner Wrench: Everything you need to know about AGM batteries

If you're thinking of upgrading to an AGM battery, read this first

Brian Turner

Oct 27, 2020 • May 19, 2021 • 2 minute read • Join the conversation

Need a new battery? You might want to go AGM with your next one. Photo by Supplied /iStock.com via Getty Images

If you’re driving something 2014 or newer and have to replace its battery, you might have gotten some AGM sticker shock. AGM stands for Absorbed Glass Mat and in batteries, it refers to a totally new design driven by higher needs in vehicles equipped with a ton of electronics, especially those with automatic start/stop systems . Prices can be anywhere from 25 to 40 per cent more than a traditional lead/acid battery, and if your ride calls for an AGM battery, dropping in an old-fashioned type is likely to introduce more than a few problems.

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What are the benefits to using an AGM battery?

AGM batteries use a mesh of crushed fiberglass between the lead plates inside the battery and have control valves to prevent excessive loss of liquid during a recharge phase. This makes them much safer to handle and use, especially in those vehicles where they’re placed inside the passenger compartment or under a rear cargo floor.

There are other benefits, too: they can offer more starts per lifetime (up to 60,000), whereas a conventional battery is usually good for around 5,000. They can also recharge faster, which is important for vehicles that see a lot of short runs at lower speeds, and their construction is usually more durable thanks to the glass matting that can help cusion the battery’s internals from severe road shocks. Finally, the control valve which keeps evaporated liquid from venting out will also help extend the lifespan.

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What are the drawbacks?

They don’t take kindly to the wrong type of battery charger. While you can use traditional battery chargers to recharge an AGM battery, to avoid overcharging and damaging the unit, low power settings between one and 12 amps are best.

Not every batter type is available in AGM

Batteries are specified by group numbers denoting their physical dimensions and post configurations. The other main spec to keep in mind is the CCA (cold crank amperage) rating; this is the electrical power a properly charged battery will deliver at around -18°C. For example, if a vehicle originally called for a battery with a 500 CCA rating, replacing it with something with a more powerful 600 CCA rating is a good idea, because as starters and alternators age, a little extra boost is needed.

Is an AGM battery worth it?

If you do the math, you could easily justify spending 25 to 40 per cent more for a battery that would last at least twice as long, withstand some rough road treatment, and recharge faster on short runs. And for something that’s less likely to blow up in your face when trying to jump start your neighbour’s car, well, that’s priceless.