A battery energy storage system (BESS) stores energy at lower demand and sends saved energy back to the system during peak load. It thus represents a good solution for daily load leveling. The evaluation of the Ampere-hour capacity of the battery needed for load leveling during a period of several hours is of great importance when using BESS as an active power peaking station. A battery simulation model that was developed for this purpose is presented in the paper. The model takes into account the battery voltage dependency on the capacity and current, and is based on the performed battery measurements at constant discharging currents. By using this model, which should prove to be a very effective tool for BESS capacity planning, the simulation of the characteristic load leveling was performed and compared to the measured voltage and current profiles.