A special class of multistage optimal control problems arises in the case of batch reactors fed by discrete instantaneous additions of raw material. The underlying differential-algebraic equations (DAEs) remain unchanged throughout the time horizon of interest, but the instantaneous additions of material are impulsive inputs that result in discontinuities in the state variables. Optimization parameters can include, among others, the amount of each charge and the reaction stage duration following each addition. In this paper, the problem of optimizing the operation of discrete charge batch reactors is addressed within a general framework that is independent of kinetic mechanisms and nonidealities. No approximation need be involved as the solution procedure is based on a general purpose robust algorithm for dynamic optimization problems.