Dynamic state empirical model of energy and power as the state variables derived from electrical behavior of a lead acid battery system is presented. The empirical model describes the relationship among the total, usable and loss of power and energy under dynamic load conditions. It has been assumed that the total energy of the system is dependant only on temperatures. On the other hand, the available and internal loss of power and energy during the operations depend on various temperatures and loads. Detailed description of experimental procedures including identification of model parameters are shown. Utilizing the model, the simulation results for the battery system including state of charge at dynamic driving conditions under various temperatures and loads were compared to that of bench tests. Good agreement of the simulation with the bench test results are shown.