Abstract: We propose an adaptive parameters equivalent-circuit model of a Li-ion battery based on multi-input multi-output (MIMO) fuzzy control to solve the problem that the normal equivalent-circuit model cannot reflect a Li-ion battery's internal state precisely at all regions of the state of charge (SOC). The model, taking the partnership for a new generation of vehicles (PNGV) model as an adaptive prototype, dynamically updates the parameters in real-time using the MIMO fuzzy regulator. The updates are made according to the difference in the external characteristics between Li-ion battery and the PNGV model, in order to reach the goal of accurate modeling and reflecting the battery's true internal state. Experiments verify the influence of adaptive parameters on the model accuracy and adaptive performance, and show the model-emulating effects under various operating conditions. The comparison of SOC error estimation applying the extended Kalman filter (EKF) between the battery adaptive parameters model and the static parameter PNGV model verifies the effectiveness of the adaptive parameters model.