A Guide to AGM, or Absorbent Glass Mat Batteries


You’ve probably heard of the AGM battery, which stands for Absorbent Glass Mat. But what exactly does Absorbent Glass Mat (AGM) represent, and how does it improve battery performance over normal lead acid batteries?

Let’s go through the fundamentals of SLA (sealed lead acid) battery building. SLA batteries are made up of lead plates (both positive and negative) and electrolytes, which are then stacked into “cells” and placed in a battery casing. Some of these batteries are also valve-regulated, allowing modest quantities of gas to escape during the recombination process during charging. Although these batteries allow gases to escape, they are spill-proof (also known as valve-regulated lead acid or VRLA) and may be used in nearly any position (the only limitation is they are not recommended to be used upside down). Because they are sealed, no electrolyte is required after manufacturing, and any gases produced enter a recombination cycle.


The construction of AGM batteries is similar to that of regular SLA batteries, with the addition of a fiberglass mat that is put between each negative and positive plate to absorb the electrolyte. The battery becomes non-spillable because the mat behaves like a sponge with the electrolyte.

The AGM battery keeps the electrolyte in place by allowing it to travel through the fiberglass mat, producing the largest surface area for the electrolyte to hit the plates without flooding the battery. AGM batteries only have enough electrolytes to keep the mat moist, and if the battery breaks, there is no free liquid to flow out. This allows for less electrolyte in the battery while producing the same energy as regular SLA batteries.


Most people think about AGM batteries in terms of deep cycle battery applications. Not all AGM batteries, however, are deep cycles. While AGM batteries are popular for deep cycling because they have a depth of discharge (DoD) of 80% vs. a normal flooded battery’s DoD of 50%, they are also popular for starting batteries. This is due to its low internal resistance and ability to generate high current loads quickly. AGM batteries are also utilized as start-stop batteries in current vehicles since flooded batteries are not strong enough to withstand the frequent cycling in start-stop applications, which might lead the battery to fail after only a few years of service.

At Space Flight Power, for example, we provide AGM technology in deep-cycle AGM batteries (the PDC series) and as a popular choice in our Power Sport family (Super Sport, Ultra Sport AGM, and our Stop-Start AGM lines). However, AGM is our technology in our general purpose (PS) and long life (PG) product lines since the Absorbent Glass Mat separator optimizes electrolyte surface area, boosting battery performance.

Because each cell in an AGM battery contains two volts, AGM batteries come in various voltages, including popular 6V and 12V types.


There are several distinctions between AGM and lithium batteries. When selecting the correct battery for your application, you must first understand what you want from the battery. Is it a deep cycling, high rate discharge, or float standby application? Is there a built-in charger for a certain chemical in the application? What is your financial situation? Etc.

Space Flight Power has compiled a detailed reference to the differences between sealed lead acid batteries and LiFePO4 batteries, which should help you determine if AGM is the better choice for your application. To summarise, depending on the application and your budget, AGM batteries are preferable to flooded cell types because of their reduced weight, lower maintenance, and improved performance. AGM batteries are also preferred over Gel batteries since they are far more prevalent and typically less priced. The choice between AGM and lithium batteries will be determined by your application and what you want from the battery.