On This Day in Telephone History December 15TH 1888 – Patent issued to Hammond V. Hayes, later chief engineer, AT&T Company, on the common battery switchboard. In earlier telephone systems, each telephone was equipped with a set of batteries which required constant testing and replenishing. The common battery switchboard made it possible for one main battery at the central office to supply current for nearly all telephones connected to it. A few telephones at great distances from the office may need supplemental batteries.
