Three Misconceptions About AGM Batteries

More batteries are moving into the trunks and under the seats of some vehicles. If the battery is not under the hood, chances are it’s an absorbent glass mat (AGM) or gel cell battery. AGM batteries eliminate acid spilling in accidents because they are sealed. They can also be installed at odd angles.

Battery Manufacturers can shave off a few pounds from the vehicle because these batteries pack a lot of power for their size and weight. That’s a big ­reason why they are being found more and more on late-model vehicles.


Here are three misconceptions about AGM batteries:


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

False. These batteries like to be charged slow and low. Many AGM/gel cell battery chargers have microprocessors that collect information from the battery and adjust the current and voltage accordingly. Some have different settings for charging flooded, gel and 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.


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

False. 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.



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 vehicles have a Battery Sensor Module or 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.