A battery discharge model is developed to predict terminal voltage and current for a constant-power discharge. The model accounts for the impact of discharge rate on the effective capacity. The model utilizes empirically-determined coefficients, easily obtainable from product data sheets. The model is intended to provide estimates for initial predictions and system sizing; total computational and engineering costs to develop the inputs and obtain results are low. Comparison of model predictions with experimental data in the development and testing of alkaline primary cell battery packs shows good agreement. Published by Elsevier Ltd.