Improvement of battery pack efficiency and battery equalization based on the extremum seeking control

•A model-free and adaptive optimization method, extremum seeking control(ESC), for improving battery equalization and efficiency of Lithium-ion battery pack is initiated.•The proposed method can improve both battery equalization and efficiency where efficiency for each cell is unknown and operation conditions are varied under different power loads and different external conditions.•The existence of extreme efficiency and optimal current under different power loads and different external conditions for battery pack has been proved.