A method for predicting power capability of a battery pack in a system includes determining an open-circuit voltage of the battery pack via a controller, calculating pack resistance using measured voltage and current during a charge or discharge event, and calculating a maximum current of the pack using the open-circuit voltage and internal resistance. The method includes selecting the lower of an absolute value of each of the calculated maximum discharge current and predetermined current limit, calculating the discharge power capability of the battery pack using the selected lower absolute value, and controlling a state of the system using the calculated power capability. The method also controls the charging current and parameters during a DC fast-charging operation. A system includes the battery pack, electric machine, and controller. The system may be a vehicle having an electric powertrain, with an electric machine powered by the battery pack.