A single electrical power source used to energize more than one circuit, component, equipment, or system. Note 1: A common battery is usually an electrolytic device and is usually centrally located to the equipment that it serves. Note 2: In many telecommunications applications, the common battery is at a nominal -48 Vdc. Note 3: A central office common battery supplies power to operate all directly connected instruments. Note 4: Common battery may include one or more power conversion devices to transform commercial power to direct current, with an electrolytic battery floating across the output.