Rick's Free Auto Repair Advice

Upgrade to an AGM car battery?

Should you upgrade to an AGM battery?

Generally speaking, if your car or truck didn’t come with an AGM battery, you have be cautious about upgrading to an AGM battery because AGM batteries require a different charging routing. However, if your car or truck did come with an AGM or you have a start/stop system, you must replace it with an AGM battery. In fact, installing a standard lead-acid battery in a car or truck that requires an AGM battery can cause the new battery to explode. Yeah, not kidding.

Can your vehicle handle an AGM battery upgrade?

AGM batteries require a different charging routine than standard flooded lead-acid SLI batteries. Late model vehicle equipped with a power management system and a current draw sensor can usually handle an upgrade to AGM. These power management system constantly monitors current draw and the state of battery charge. They charge the battery using different protocols to maintain the life of the battery. See this article to learn how the GM power management system charges the battery based on it’s level of charge and sulfation

Late-model cars and truck relay on the PCM/ECM to command the charging rate and that software is configured based on the battery type that was installed at the factory. If you install an AGM battery, your alternator can overcharge it and shorten its life.

However, upgrading to an AGM battery in an older vehicle without a power management system can actually damage the AGM battery by overcharging it. AGM batteries generally require charging at a lower voltage and for longer periods; low and slow is how you charge an AGM battery.

Differences between an SLI and AGM battery

Traditional starting/lighting/ignition (SLI) batteries are designed to provide a quick burst of high amperage energy to crank the engine, even when it’s very cold. Because the plates sit in a liquid electrolyte bath, they are referred to as “flooded lead-acid” batteries. SLI batteries must be mounted in an upright position or the electrolyte will spill out.

Absorbed glass mat (AGM) batteries, on the other hand still have lead plates but they’re not sitting in a bath of electrolyte. Instead, the plates are separated by a fiberglass mat that absorbs the electrolyte and wicks it to the plates. Because the electrolyte isn’t pooled, an AGM battery won’t spill if knocked over, and it can be mounted in different positions. It can also be transported without the hazardous material restrictions required by SLI batteries.

Why buy an AGM battery?

AGM batteries have a lower self-discharge rate

All lead-acid batteries self-discharge over time. AGM batteries have a lower self-discharge rate than SLI batteries, so you can leave them longer without starting the vehicle.

AGM batteries have lower internal resistance

The internal plate chemistry and bus bars provide lower internal resistance which translates into more power from a smaller battery. In many cases, an AGM car battery will be smaller and deliver more power than a comparable flooded lead-acid SLI battery

They’re more resistant to sulfation and degradation

All car batteries are susceptible to sulfation, but AGM batteries don’t sulfate as easily as flooded SLI batteries. What causes battery sulfation?

A AGM battery charges charge faster than an SLI battery

An AGM battery can accept a charge up to five times faster than an SLI battery.

They can survive a deep discharge better than an SLI battery

AGM batteries can be discharged up to 80% without damage.

Start/stop applications require an AGM

NEVER install a flooded lead-acid battery in a vehicle with start/stop technology—EVEN IF YOU’VE TURNED OFF THE START/STOP FEATURE!!! The charging system is designed for AGM. A flooded lead-acid battery can explode if installed in a start/stop vehicle.

©, 2019 Rick Muscoplat



Posted on by Rick Muscoplat


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