A mixed‐reaction model has been developed to simulate the discharge behavior of cylindrical alkaline zinc‐manganese dioxide primary cells. The analysis of the system considers a whole prismatic cell consisting of a zinc amalgam anode, an inert porous separator, and a manganese dioxide cathode. The domain of investigation extends from the anode to the cathode current collector. The model is based on a macrohomogeneous theory of porous electrodes and includes considerations for the ohmic potential drop, diffusion and convection in the electrolyte, change in porosity and electrolyte composition due to chemical and electrochemical reactions, charge‐transfer effects, and ionic transport in a concentrated electrolyte. The anode is considered to be a reversible, nonpolarizable electrode with two anodic reactions occurring simultaneously. A parameter which is based on the ratio of the extent of the two reactions is used to characterize the anode‐mixed reactions. A solid‐state proton diffusion as well as a direct charge transfer are used to describe the cathodic reaction. The performance between cells of different sizes is compared at the same galvanostatic discharge rates per unit cathode mass. Sources of polarization are identified, and the influence of cell behavior by the different operating variables are examined.