This paper describes a number of improvements that have been made to the battery model that is used in the Hybrid2 hybrid power system simulation model. The improvements consist of (1) a more complete implementation of the Kinetic Battery Model, on which the Hybrid2 battery is based, and (2) extensions to the original battery lifetime model to more accurately predict battery lifetime. The enhanced implementation consists of adding the capability to determine the Kinetic Battery Model voltage constants from charge and discharge test data. The lifetime model improvements were inspired by a EU/US hybrid power system component Benchmarking Project, and were added so that lifetime predictions (1) could be more readily assessed and (2) would more closely reflect experimental results. The original Kinetic Battery Model lifetime prediction employs a damage model analogous to that used to assess material fatigue. It uses a cycles to fa ilure vs. depth of discharge curve, together with a rainflow cycle counting algorithm to calculate damage from time series state-of-charge values. The damage is then used to predict lifetime. The modified lifetime model considers (1) mean value of each cycle and (2) cycle discharge rates. The work has also resulted in a free-standing battery model, outside of Hybrid2, which can be used with state-of-charge time series derived from other models or field test data. This paper summarizes the work that has been completed and shows comparisons between the model’s predictions and recently obtained Benchmarking results.