In telecommunication, a common battery is 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.
Source: from Federal Standard 1037C and from MIL-STD-188
