A battery system includes a battery module, an active cell balancing circuit, and a battery controller. Each cell has diametrically-opposed positive and negative cell tabs. The circuit includes voltage sensors and, at each end of the battery module, first and second tiers of switches and an energy storage element. Each voltage sensor is located between a different pair of adjacent cells. The controller receives measured voltages from the sensors indicative of an electric potential between adjacent battery cells. Responsive to the measured voltages, the controller commands the first tier to selectively connect or disconnect designated pairs of cells to the corresponding second tier. The controller also commands the second tier to selectively connect or disconnect the designated cells to a corresponding energy storage element. This action shuttles energy between the designated pairs of battery cells to balance a state of charge.