AGM Battery (Absorbent Glass Mat)
A sealed, maintenance-free lead-acid battery type in which the electrolyte is absorbed and held in a glass fibre mat separator. Because there is no free liquid electrolyte, the risk of spillage in a rollover is low and the battery can also work lying on its side.
In an AGM the plates and the glass fibre mat are pressed tightly together. This structure lowers the internal resistance, so the battery can deliver high current with less voltage sag than a flooded lead-acid type. Because the sealed case recombines the gas released during normal charging inside the cell, it is more suitable for use in the living area.
On the charging side AGM is a chemistry with a relatively narrow voltage tolerance. For a 12 V battery the absorption voltage is typically given in the range 14.4-14.8 V and the float voltage 13.4-13.8 V; the manufacturer's datasheet is the authority for exact values. Overvoltage causes water loss, and in a sealed case the lost water cannot be replaced.
In an RV, AGM is chosen as a middle path between lead-acid and lithium: it needs no maintenance and withstands deep discharge better than a flooded type, but its weight and the 50% DoD limit remain on the lead-acid side. On short, high-current loads such as levelling, its low internal resistance is a clear advantage.
The context in which this term is used: RV automatic levelling guide