What is an AGM battery?

AGM (Absorbent Glass Mat) Batteries use different technology compared to lead acid batteries. It uses a fibre Boron-Silicate glass separator which absorbs the electrolyte.  AGM batteries are spill proof.

How do AGM batteries work?

During the charging of AGM batteries, Hydrogen and Oxygen is generated, and due to the presence of small catalysts the hydrogen and oxygen combines to form water. The recombining results in nearly zero water loss and wears out heat generation too.The charging techniques and voltages used for charging AGM batteries are similar to standard batteries. Therefore there’s no need to purchase a special charge controller or any other control equipment.Since the internal resistance of an AGM battery is low, it doesn’t generate much heat and offers a high current during demands. The battery generally charges quickly and its discharge time is low - up to 1% to 3% per month, which allows long durability and reliability.

How to charge an AGM battery?

The following techniques can be utilised for charging the battery:

Float or Stand By

This way the battery is continuously under charge. It is recommended to keep the voltages lower than regular charging or cyclic charging so as to prevent battery damage.  The float or stand by charging voltage varies between 2.25-2.3 volts/cell or 13.2-13.7 volts for the battery.


Cyclic type of charging is used when the battery is discharged and then charged repeatedly.Cyclic charging of an AGM battery should be of definite time otherwise overcharging may cause damage to the battery.The voltage is about 2.4-2.5 volts/ cell, or up to 14.7 volts. The advantage of using 14.1 – 14.2 volts is a longer service life of the batteries.The battery life depends upon the continuous charging and discharging cycles. When you notice that the stand-by capacity of the battery is reducing, it is an indication that you’ll need to replace the battery at a certain point.

Solar charging

You can use a solar panel to charge an AGM battery. There are two things to keep in mind:
  1. The solar panels should provide sufficient voltage (V) to charge the battery.
  2. The charging through the solar panel should be regulated with a charge controller, so as to avoid battery damage in case of overcharging.

Major advantages of AGM batteries

Some of the top advantages that AGM batteries offer over other batteries are:
  1. Spill proof
  2. Low internal resistance
  3. Fast Charging
  4. Operates under cold temperatures
  5. Standard charging techniques
  6. Can be used as a jump start, and compatible with all types of cars, 4WD, caravan, camper, motor home, truck, military uses and standby uses.

Limitations of AGM batteries:

  1. Higher cost than lead acid battery
  2. Sensitive to overcharging

Don’t combine Electrolyte batteries with AGM batteries

It is not recommended to combine electrolyte batteries with AGM batteries for the following reasons:
  1. While considering simultaneous charging of AGM and wet cell, the system will do one of two things:It will either keep charging the wet cell until it is fully charged or it may over-charge the AGM. Further, it may turn off when the AGM is fully charged while it would leave the wet cell battery only partially charged.
  2. When a wet cell battery is undercharged, it would draw power from the AGM battery. This would lead to reduced lifetime of both batteries due to undercharging and draining.
darrell wait

darrell wait

on 26 May 2021

great advice in plain english that most people would understand. thankyou Darrell

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