What is an AGM Battery?

What is an AGM Battery?

AGM batteries were created in the 1970s for military equipment. The devices were used in boats, submarines and airplanes. Subsequently, models designed for cars appeared. They quickly gained popularity due to their high performance and efficiency.


Differences of AGM batteries from other models

AGM batteries have a number of fundamental differences from lead-acid batteries. There is no liquid electrolyte in them, but there is a thin fiberglass mat impregnated with an electrolytic solution. It is located between the plates. The electrolyte contains sulfuric acid, just like in other batteries. The name of the technology stands for Absorbent Glass Mat or absorbent fiberglass mat. The electrolyte from it is supplied to the battery plates as needed. Compared with other batteries, devices of this type are distinguished by:

  • Reliable plate protection, ensured by the cushioning properties of the fiberglass interlayer;
  • A valve that prevents evaporating water from escaping from the battery case and electrolyte loss;
  • A long service life, which is 10 years, while lead batteries have an average of 5 years;
  • Strict compliance with the dimensions and geometry of the grid due to the manufacture by stamping.


The AGM battery design provides for a sealed case made of impact-resistant plastic. This ensures resistance to shaking, vibration and other mechanical damage, and prolongs battery life. Such batteries can be used in vehicles equipped with a Start/Stop system. They provide numerous engine starts in a short time.


By design, the batteries are divided into two groups. The first includes models with spiral laying of fiberglass mat. The second group includes plate batteries, which have become more widespread. The VRLA marking on a battery indicates that there is a high-pressure valve inside. The abbreviation SLA means that there’s a vent cap or a plug.


What is an AGM Battery?


Advantages of AGM batteries

The absence of liquid electrolyte in AGM automotive batteries prevents the solution from leaking when tilting or turning the device. The batteries can work in almost any conditions, but continuous inverted position may result in contact with metal elements or safety valve overlap. AGM batteries have other advantages as well:

  1. Reliable protection of the plates – the absence of liquid evaporation prevents the formation of corrosion and significantly reduces the sulfation risk;
  2. Efficiency – this is facilitated by a larger number of plates with compact battery sizes, in which fiberglass also performs the functions of a separator;
  3. Resistance to high and low temperatures – there is no liquid in AGM batteries that can expand in the heat or freeze in the cold;
  4. Resistance to deep discharge – in such situations, the battery does not fail, its operability is restored.


Reviews of AGM batteries confirm that such batteries ensure smooth operation of electronic systems installed in contemporary vehicles. They are designed for a large number of charge/discharge cycles and succeed in starting the engine in any situation.


What is an AGM Battery?


The sequence of operations when charging an AGM battery

The process of charging an AGM battery deserves special attention. Such devices are sensitive to incorrect connection and may fail when using a faulty charger. You should choose the exact amperage to charge your battery safely. To charge such a battery, the following actions should be taken:

  • Connect the battery to the charger, set the zero amperage and the nominal voltage value;
  • Connect the negative and positive battery terminals, make sure that the polarity is correct;
  • Adjust the charger to supply current within 10% of the battery voltage designed by the manufacturer;
  • Disconnect the battery from the device as the amperage approaches zero.


When the battery is properly connected to the charger, the voltage will increase and the amperage will decrease. Always check the temperature of the case during charging, the battery must not overheat. In case of heating, the device should be switched off immediately to avoid damage. Do not jump start AGM batteries with the help of other vehicles and charge the battery that has just been brought in from the cold.


The best way to charge an AGM battery is to purchase a charger designed specifically for such models. You can use chargers that have a separate mode for this purpose.

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