A vehicle may include a controller programmed to charge and discharge a battery according to an upper power limit that is based on estimates of ion-concentration profiles in the battery. The controller may be programmed such that for a given state of charge and temperature of the battery, the upper power limit increases as the profiles flatten. The upper power limit may be further based on a difference between a predefined expected power capability limit at the given state of charge and a power capability limit estimated from a voltage output and current input associated with the given state of charge.