Balancing charge between battery pack system modules in a battery

A computer program product, comprising:

• a computer-readable medium comprising:
• code to detect that a first battery pack system module comprising a plurality of battery cells is at a first state of charge and a second battery pack system module, connected in series with the first battery pack system module, is at a second state of charge lower than the first state of charge;
• code to activate, by the first battery pack system module, a first charge switch in the first battery pack system module to physically disconnect and to prevent further charging of the first battery pack system module after detecting that the first battery pack system module is at a first state of charge higher than a second state of charge of the second battery pack system module;
• code to activate at least one shunting resistor in communication with at least one battery cell in the first battery pack system module to discharge the plurality of battery cells of the first battery pack system module;
• and
• code to deactivate the at least one shunting resistor in communication with the at least one battery cell when the first state of charge of the first battery pack system module becomes approximately equal with the second state of charge of the second battery pack system module.