System and methods for determining performance degradation of a battery system are presented. In certain embodiments, the disclosed systems and methods may involve testing, monitoring, and/or modeling of battery system cyclic performance degradation at a single battery system operating temperature. The disclosed systems and methods may offer certain efficiencies over conventional techniques for determining cyclic degradation of a battery system. Such efficiencies may allow the disclosed systems and methods to be implemented in connection with real-time battery state estimation methods.