Home > Frequently asked questions > Frequently asked questions

What are AGM and gel batteries?

AGM (Absorbed Glass Mat) and gel batteries are both examples of VRLA (Valve Regulated Lead-Acid) batteries. They are also known as SLA (Sealed Lead-Acid) batteries. These abbreviations refer to the safety valves in the battery’s lid. In common parlance, the term gel battery is used to indicate both AGM and Gel batteries. AGM batteries may also be called “membrane”, “starved electrolyte” or “dry” batteries.

What are the differences between AGM and gel batteries?

VRLA batteries come in two distinct versions: AGM batteries and gel batteries. In the gel battery certain elements – often specific mixtures of silicon – are added to the battery acid, transforming the electrolyte into a gel-like substance that cannot leak. By “drilling” channels in the gel, gaseous oxygen moves from the positive plate to the negative plate. Here it encounters hydrogen gas and recombines into water, releasing energy. Gel batteries have excellent capacity, but their slightly increased acid resistance makes them less suitable for use as starter batteries. They are highly resistant against excessively deep discharge, retaining function even when the battery is discharged to 20% of its nominal capacity.

In AGM (Absorbed Glass Mat) batteries the electrolyte is held in place by a separating membrane. This is why these batteries are also known as membrane batteries. The membrane consists of a fiberglass mat and functions as a sponge. This function is based on the capillary properties of the membrane. AGM batteries can be produced using very thin separating membranes, leading to low internal resistance. This means that high output power can be achieved with batteries of relatively low size, making this type of battery ideal for a wide variety of applications.