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UPSs came on the scene with the advent of large commercial computers that required high quality AC power along with a reserve energy storage to continue supplying power for an orderly shutdown in the event that the primary AC power failed. At the time there were very few choices as far as the type of battery for energy storage. In the lead acid category, the only batteries available were the flooded type that was commonly used as reserve in DC Power applications. The UPS market has grown considerably, with the range of battery energy storage options now from a few watt-hours to several mega watt-hours. During this period a new type of lead acid battery, the Valve Regulated Lead Acid (VRLA) was invented. Initially these batteries were produced in the single and double-digit ampere-hour sizes. Over the past two decades the VRLA product has matured and the sizes now range up to 3000 AH for single cell units and 250 AH for six cell modules. The VRLA battery and especially the front terminal, ten year design life type have several unique features that make it an excellent choice in large UPS applications, defined as systems of 500 KVA and larger, where flooded batteries have usually been applied.