Publisher Summary This chapter discusses carbon-zinc and carbon-zinc chloride primary batteries. The electrochemical system of the carbon-zinc battery uses a zinc anode and a manganese dioxide cathode and an electrolyte of ammonium chloride and zinc chloride dissolved in water. Various grades of manganese dioxide are used for Leclanché cells. These range from the natural ores used for inexpensive low-rate cells to the synthetically produced or electrolytically prepared grades used in more expensive high-rate cells. Powdered carbon is used in the cathode depolarizing mix, usually in the form of acetylene black, to improve conductivity of the mix and to retain moisture. The standard carbon-zinc dry battery is not designed to be recharged. The basic cell is made in many shapes and sizes, but two general categories exist for round cells, which are available as unit cells or in assembled batteries and fiat cells. The zinc chloride Leclanché cell is a special modification of the carbon-zinc cell. They differ principally in the electrolyte systems used. The electrolyte in a zinc chloride cell contains only zinc chloride, while in a carbon-zinc cell the electrolyte contains a saturated solution of ammonium chloride in addition to zinc chloride. The omission of ammonium chloride improves the electrochemistry of the cells but places greater demands on the cell seal. Because of their ability to operate at high electrode efficiencies, the useful current output of zinc chloride cells is usually higher than that of carbon-zinc, and zinc chloride cells operate at high current drains for a considerably longer time than carbon-zinc cells of the same size.