An intelligent battery system senses current flowing in the direction of charge current through positive and negative terminals and battery cells of a battery pack. In response, a processor within the battery pack transmits battery parameter data to a separate output port of the battery pack. The battery parameter data includes the state of charge of the battery cells, temperature data and the type of battery pack. The processor also responds to specific data requests transmitted into the battery terminals by transmitting the requested battery parameter data. The battery pack is also designed to minimize power dissipation of the processor. When the battery pack is not subjected to either charge or discharge for a predetermined period, the processor is rendered into a "light-sleep" mode in which power dissipation is substantially reduced. The processor is awakened from the light-sleep either by a timer or by charge or discharge activity to monitor the amount of charge or discharge and other battery parameters.