US Patent 8723481 Battery pack with balancing management

A battery management system includes multiple battery modules, first balancing units, second balancing units, and controllers. Each battery module is coupled to a respective first balancing unit, second balancing unit, and controller. A first controller of the controllers controls a first balancing unit of a first battery module to adjust a voltage output of the first battery module when the first controller determines the voltage output of the first battery module is greater than a combined voltage output of the first battery module and a second battery module, and controls a second balancing unit of the first battery module to adjust the combined voltage when the first controller determines the combined voltage is greater than the voltage output of the first battery module.