Hybrid-electric and electric vehicles require information on the condition of the electric energy storage system, a quantity not directly measurable onboard because of its relation to the concentration of reactive species inside the battery cells. Mathematical models of battery systems have been developed for estimation strategies. IFP offers an integrated approach in predicting battery behavior, from improved electrochemical and thermal lumped-parameter modeling to the vehicle application as an alternative to equivalent circuit models. The approach results in advanced electrochemical modeling for both voltage and temperature prediction of battery packs under strong to zero current, while maintaining complexity of standard models and avoiding excessive computational time. Validated in various operating conditions, the models study battery performance evolution and aging and can be used to develop the management system or to design a vehicle/system simulator.