Methods of charging a vehicle battery pack are disclosed. Example methods may include determining a voltage imbalance between at least two parallel strings of a battery pack exceeds a threshold magnitude. Methods may further include electrically reducing the voltage imbalance between the at least two parallel strings using a series circuit including a first group of one or more of the battery cells of a first one of the parallel strings, and reconnecting the parallel strings in an electrical circuit in parallel to each other, in which configuration the strings of the battery pack may supply power to the vehicle.