Mono-chloronitrobenzene (MCNB) is investigated as a cathode material for magnesium reserve batteries that use a magnesium anode and a 2M magnesium perchlorate aqueous electrolyte. The composition of the conducting material (acetylene black) in the cathode mix is optimized to obtain better electrochemical performance. The reduction mechanism of mono-chloronitrobenzene is examined by means of cyclic voltammetry using a glassy carbon electrode. Discharge studies at different current drains indicate that Mg–MCNB cells exhibit the highest Coulombic efficiency (86%) at a current drain of 100mA. The reduction of MCNB to mono-chloroaniline is irreversible and diffusion-controlled.