General Features of Common-Battery System.
a. Advantages. The use of a single storage battery gives the common-battery system several important
advantages over the local-battery system.
(1) The storage battery used in the common-battery system is much more economical to maintain than the dry
cells of the local-battery system. Dry cells deteriorate and must be replaced periodically, whereas storage batteries can be
recharged when necessary.
(2) The storage battery of the common-battery system gives a voice signal more uniform in amplitude, because it
maintains a fairly constant voltage--more constant than the dry cells of the local-battery system.
(3) In the common-battery system, signaling is performed automatically when the receiver is lifted, eliminating
the need for a hand generator and manual cranking, and making the equipment of the telephone set much simpler.
(4) In the common-battery system, the operator is signaled automatically upon completion of calls. This reduces
the amount of supervision required, and allows a single operator to handle many more lines than is possible in a local-
(5) Finally, because the single storage battery is located at the telephone central office, inspectors are not required
to make periodic visits to the associated telephone stations, as they must do in a local-battery system, to test dry cells for
b. Limitations. In spite of its many advantages, the common-battery system has limitations and disadvantages
that must be considered before giving it preference over the local-battery systems in certain applications.
(1) The common-battery system requires line construction of much higher quality than that required for the local-
battery system, because current for the operation of the transmitter at the telephone set and supervisory relays at the
central office must be supplied over the line.
(2) The lines of the common-battery system must be well balanced electrically, since unbalance in the wires of
the outside plant impairs the quality of transmission and the distance over which transmission can be effected.