Abstract: Disclosed is an apparatus and method for controlling the discharge or charge power of a battery, capable of preventing over-charge and over-discharge of battery cells according to states of the battery cells, and solving a problem that the lifetime of a conventional battery pack is rapidly reduced due to the over-charge or over-discharge of some cells of the battery pack. The method includes the steps of estimating the maximum power of the battery, measuring voltage of a battery cell or pack, checking whether or not the voltage of the battery cell or pack deviates from a preset limited range so as to correspond to the maximum power, and when the voltage of the battery cell or pack deviates from a preset limited range, controlling the discharge or charge power of the battery.