Energy state of health estimation for battery packs based on the degradation and inconsistency

To identify the end-of-life batteries, the capacity and internal resistance are mostly used to evaluate the state of health (SOH) for battery cells and packs. However, these two methods may lead to a different conclusion concerning the SOH of the batteries due to the independence between the capacity and internal resistance. In this paper, the energy SOH for a battery pack is proposed and defined as the ratio of the current maximum available energy (MAE) to the rated total energy. Incorporating both the degradation and inconsistency of the capacity and internal resistance, the energy SOH is more appropriate and accurate to reflect the actual state of battery pack compared to the capacity and power SOH. The superiority of this method is shown through the data analysis and comparison of different methods.