Publisher Summary This chapter discusses magnesium-organic electrolyte primary batteries. Theoretical considerations predict that organic compounds, such as meta-dinitrobenzene (m-DNB), are especially attractive as cathode materials in primary cells. Considerable effort is spent by various battery manufacturers, including Marathon, on the development of magnesium-magnesium perchlorate-meta-dini trobenzene cells. They are made with a cylindrical structure similar to that used with the manganese dioxide-magnesium perchlorate dry cells. The organic cell requires the use of a higher surface area electrolyte absorbent to be mixed with the meta-dinitrobenzene that is used with manganese dioxide. Also, the ratio of the meta-dinitrobenzene to carbon black is lower and the water content is higher than for the manganese dioxide cell. Water participates in the electrochemical reaction of the meta-dinitrobenzene cell by supplying hydrogen and hydroxyl ions. The operating voltage of this cell is lower than for the other dry cells; however, it has a fiat discharge curve. Up to 121Wh/kg have been obtained in practice for an A size cell at 21°C at the 25 h rate, compared to 100Wh/kg for the equivalent size manganese dioxide-magnesium perchlorate cell.