AGM Batteries: Myths And Truths

AGM Batteries: Myths And Truths

Test your knowledge of AGM batteries.

Have you noticed more batteries are moving into the trunks and under the seats of some vehicles? Chances are, if the battery isn’t under the hood, it’s an absorbent glass-mat (AGM) or gel-cell battery. AGM eliminates acid spilling in an accident because it’s sealed. They can be installed at odd angles.

These batteries pack a lot of power for their size and weight, which
allows manufacturers to shave off a few pounds from the vehicle. That’s a big reason why they’re being found more and more on late-model vehicles. Also, these batteries have a greater reserve capacity to support stop/start systems and key-off functions.

Here are four AGM myths you may have heard.

1. You can use your regular battery charger on AGM or gel-cell batteries.


These batteries like to be charged slow and low due to differences in internal resistance.

Many AGM battery chargers have microprocessors that collect information from the battery and adjust the current and voltage accordingly. Some have different settings for charging flooded or AGM batteries. Overcharging can kill these batteries. Also, alternators are not chargers. Don’t rely on an alternator to do the work of a charger. If a battery is discharged to the point that it cannot start the vehicle, use a charger as soon as possible to make sure the battery gets fully charged.

2. AGMs and gel cells can be tested the same way as conventional batteries.


These types of batteries have lower internal resistance than flooded batteries. Older capacitance battery testers/analyzers may not be able to accurately read these batteries. Most new battery analyzers have a special mode for AGM/gel-cell batteries. Old-school load testers might not provide conclusive results.

Using a multimeter to measure the state of charge is not the same as a conventional flooded battery. After the surface charge is removed, the voltage of an AGM with 100% state of charge might be 13 volts. A flooded battery might have only 12.6 volts.

3. AGM or gel-cell battery replacement is the same as flooded-battery replacement.

True and false.

While the installation of the battery may be the same for the two battery styles, some vehicles require an extra step to tell the vehicle that the battery has been replaced.

Newer GM vehicles have a battery-sensor module on the negative battery cable. Ford has the battery-monitoring system (BMS). Other manufacturers have similar systems. These systems require recalibration with a scan tool if the battery is replaced. If the system is not recalibrated, the alternator might overcharge the new battery and cause the battery to fail soon after replacement.

Some vehicles can perform a self-learn for the battery by measuring the internal resistance of the battery. But, often a scan tool can force the procedure so you know there will be no issues with the battery.

4. You can’t upgrade a customer to an AGM battery if the vehicle originally came with a flooded battery.


You can install an AGM battery into a flooded-battery application. An AGM battery will give the vehicle more cold cranking power and greater resistance to heat and vibration. You never want to downgrade a vehicle that came with an AGM battery to a flooded battery.

You May Also Like

Do You Suffer From CED? Good News – It’s Curable

The creep of Customer Experience Decline can take hold if you allow your shop to lose focus.

In business, as in life, mistakes WILL happen. How you respond will make the difference in whether your customer will remain loyal and continue to do business with your store. Customer relations are easy as long as things go well – when they don’t, you and your team have the opportunity to shine or look like the proverbial pile of…well, you know. 

Tool Time Podcast: CTA Tools

Nadine Battah and Eric Garbe learn about CTA Tools’ history and innovative technology.

The Purge: Flushing & Filling the Coolant

This job isn’t needed as often as it used to be, but it’s still important.

ADAS: Coming of Age

Driver-assist systems are categorized into levels, determined by the amount of automation for any given system.

Minding Your P’s And Q’s

Price and Quality are two of the most important considerations for customers purchasing from you.

Other Posts

Can You Jumpstart an EV?

How can an EV battery go dead? It’s likely the 12V battery powering everything else that’s the culprit.

Clarios Formalizes Joint Development Agreement with Altris

Partnership will develop sodium ion cells for low-voltage battery technology systems, software and integration.

Toyota Explores Lithium-Ion Battery Recycling

The joint research project with Argonne National Labs seeks to utilize a new process for recovering critical battery materials.

Tool Intel – Understanding Air Tool Fittings and Couplers

Why don’t air tools come with fittings installed? Here’s why customers need to buy what they actually need.