Conventional lead acid batteries are the base load of the industry. But the liquid sulfuric acid inside them is not ideal for all conditions. It can burn skin and damage surfaces if it leaks out. By comparison, absorbent glass mat (AGM) batteries stabilize the acid electrolyte in glass fiber mats. Moreover, we can install them in any orientation because the electrolyte cannot flow away from the plates.
Do Absorbent Glass Mat Batteries Use Different Technology

AGM, lead-acid, and gel-type batteries all use the principle of lead plates on either side of a diluted acid separator. However, absorbent glass mat batteries immobilize the solution as opposed to flooding the casing.
The mats that do this do not actually absorb the sulfuric acid. If they did, the electrons would not be able to flow freely between the plates. Instead, the extremely thin fibers contain it in the mesh like a sponge.
This difference in electrolyte containment means the lead plates no longer need to be flat. Of course, they could be, but we could also bend them, or roll them into a spiral. Despite this, absorbent glass mat batteries are always inside a conventional battery case. This makes them interchangeable with other designs.
So Why S0 Many Lead-Acid Batteries in Circulation

AGM batteries charge considerably faster than conventional lead-acid ones. Rapid charging in turn reduces the likelihood of undercharging leading to shrinking capacity.
So on paper we should all be buying them. But we don’t, because AGM batteries can be twice as expensive as conventional flooded-cell ones.
Instead, we save them for special occasions, like stunt motorcycles and airplanes that turn batteries upside down. Their vibration resistance makes them ideal for aggressive motorsport too. In addition their lower hydrogen discharge rate makes them safer for indoor applications. Finally, they excel on the frozen wastes of the Arctic. Because they don’t have free electrolyte to freeze, expand, and burst the casing.
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Preview Image: Opened AGM Battery