Valve Regulated Lead Acid battery. AGM and Gel are the two types of VRLA batteries. These batteries have no “free” liquid electrolyte and in the cell operate on the oxygen recombination cycle, which is designed to minimize water loss. VRLA Advanced American Technology and the use of the most modern computer-aided design and manufacturing techniques combine to make MK Battery’s Sealed AGM Batteries the standard by which all other AGM batteries are measured.