A type of battery used in older vacuum tube-based radios to provide power for the tube plates and screens, in situations where alternating current (AC) power was either unavailable or undesirable. Its use gave rise to the term "B+", to denote the plate and screen voltage in a radio receiver.
B batteries were available in standard voltage ratings of 22½, 45, 90, or 135 volts. The battery itself was made up of a number of 1.5-volt cells (smaller versions of the usual "flashlight" battery), housed in a container, to produce the required voltage: 15 for the 22½ -volt battery, 30 for the 45-volt, 60 for the 90-volt, and 90 for the 135-volt. In typical receiver service, the life of a B battery was dependent on many factors: efficiency of the tube types used in the receiver, hours of usage by the consumer, and the quality of the battery itself. Even so, battery life was generally measured in months and the radio listener could, with care, expect reasonable service from the receiver.
Until the advent of AC-powered radios in the late 1920s, almost every receiving set obtainable required battery power. After AC sets became commonplace, battery power was relegated to use in farm radios designed for areas without AC service, and in portable radios. Starting in the 1950s, the B battery disappeared from use with the coming of transistor radios that required neither plate nor filament voltages. Higher-voltage batteries are still available today, but are used mainly in photographic and alarm-system applications.
SOURCES
Ghirardi, Alfred A., Modern Radio Servicing. New York: Radio & Technical Publishing Co., 1935.
Kendall, Lewis F, Jr., and Koehler, Robert Philip, Radio Simplified. Philadelphia: The John C. Winston Company, 1925.