Oldham type CVG3 radio accumulator, c 1934-1939.
© Science Museum / Science & Society Picture Library
This two-volt battery was produced between 1934-1939 and again, after WW2, between 1948-1960. An accumulator is a lead-acid system, with plates of lead oxides and an electrolyte of sulphuric acid, and is the type of battery widely used to start car engines. Each cell produces two volts of direct current.