Abstract: The present invention provides an actively rapid battery voltage balancing system which includes a power converter, a switch, a voltage balancing multiplexer, a voltage measurement multiplexer, a voltage sensor, a microprocessor, and a series connected battery pack. By the application of the above components, the balancing voltage conditions of each battery cell in a series connected battery pack can be actively monitored and estimated. While in the charge or discharge period, if a battery cell in the series connected battery pack is determined to be an unbalanced cell, the voltage balancing process can be carried out promptly. Less component is required to fulfill the purpose of the cell voltage balance in the present invention.