Abstract Battery State of Power (SoP) estimation is one of the most crucial tasks of the battery management system in electric and hybrid electric vehicles. The inevitable error in estimates of battery State of Charge (SoC) and State of Health (SoH) is a cause of inaccuracies towards estimating the SoP for an aged battery. To overcome this, the present study aims to propose a new approach for predicting an aged cell SoP in which no a priori knowledge of battery SoH is required and the estimation method is robust to inaccuracies of SoC estimates. Accordingly, a combined reference mode of constant-current and constant-voltage is utilized to estimate fresh cell SoP which is then adapted to various aging states using a model-less control system. The control system, which belongs to a class of fuzzy logic-based controllers, benefits form a closed-loop framework leading to a more reliable and accurate SoP estimate. For verification, an experimental setup comprised of fresh and aged LiFePO4 cell samples is designed and the extracted data are utilized in a Model-in-the-Loop simulation for a hybrid electric vehicle. The results demonstrate the improved accuracy and robustness of SoP estimation while achieving a guaranteed safe operation of battery.