Rick's Free Auto Repair Advice

AGM car battery

Should you buy an AGM car battery?

Do it yourselfers have more choices than ever before when they shop for a new car battery, including the newer and most expensive AGM car battery. Generally speaking, if your car or truck didn’t come with an AGM battery, there are some very good reasons why you shouldn’t switch to an AGM style. 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.

Differences between an SLI and AGM battery

Traditional starting/lighting/ignition (SLI) batteries is designed to provide a quick burst of high amperage energy to crank the engine, even when it’s very cold. SLI batteries have thinner lead plates than a deep cycle marine battery and more of them, so more of the lead is exposed to the liquid electrolyte. 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 free flowing 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 free flowing, 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.

What are the Pros of 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 and stores can leave them on the shelf longer without having to charge them.

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?

They charge faster

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

They can accept a deeper discharge without damage

AGM batteries can discharge up to 80% without damage.

But, AGM batteries shouldn’t be installed in all applications

AGM batteries require a different charging routine than standard flooded lead acid SLI batteries. If you own a late model vehicle with a power monitoring feature but the vehicle does not require an AGM battery, you should NOT install one. 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 it’s life.

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


Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN