Absorbent Glass Mat Batteries or AGM Batteries are part of the VRLA (Valve Regulated Lead Acid) battery family. Most popular in the 1980’s, AGMs were used in military grade vehicles along with UPS applications.

AGMs are close in design to Flooded Lead Acid Batteries. The main differentiation is that the electrolyte is contained in the battery by being absorbed into extremely porous microfiber glass separators, which are located between the batteries electrodes.

The process of absorption makes AGMs a maintenance free battery that is lightweight and more desirable, and VRLA (AGM or GEL) batteries can be installed without the fear of spilling the electrolyte.  The formula of such a reaction is found as:

Formula for Lead Acid Battery during Discharge: PbO2 + Pb + 2H2SO4 → 2PBSO4 + 2H2O

Formula for Lead Acid Battery during Re-Charge: 2PbSO4 + 2H2O → PbO2 + Pb + 2H2SO4

Because of their lightweight and power, AGM and VRLA batteries are used for:

-Heated seats

-Windshield wipers

-Starter batteries for high-end motorcycles


-Racing vehicles (because they are lightweight)

-Start-Stop Ignitions (due to the battery’s capability to have deep charges)

The AGM battery type has some advantages over the Flooded Lead Acid Battery because it is spill proof, can recharge faster and can withstand the elements of a harsh cold climate.

The battery, however, may not perform as well in extreme heat due to the phenomenon of “thermal runaway” because the electrolyte is not free flowing as in Flooded Lead Acid Batteries and the battery may die prematurely because the electrolyte evaporates causing the battery to dry out.