Abstract: An apparatus for battery equalization of a battery pack for use in a vehicle includes cell stack separators and cell balancers. The battery pack includes a power supply system, a plurality of cells and a plurality of cell stacks. Each cell stack includes a plurality of the cells connected in series. The cell stacks are connected in parallel to form the battery pack. Each cell stack separator is adapted to separate the corresponding cell stack from the power supply system if the difference between the maximum and the minimum of calculated internal resistances of the cells in the cell stack is greater than a predetermined threshold value. Each cell balancers is adapted to perform a battery equalization control for the cells in the separated cell stack.