A battery that serves as a single source of electrical energy, in the form of direct current (DC), for more than one circuit and perhaps for more than one connected device.The common battery may supply energy for an entire system, such as a central office (CO) or PBX, and the circuits connecting that system to terminal devices. In a telephone company application, the common battery provides loop current for the CO and a great many local loops. In many telecommunications applications, the common battery is 48 volts (V). See also battery, circuit, DC, electricity, energy, local battery, local loop, loop current, and V.