A power control system of a vehicle has a battery, an alternator, and a battery condition detecting device. The device has detecting units detecting the battery current supplied to or discharged from the battery, the battery voltage and the battery temperature, a communicating unit receiving conditions of the alternator such as power generation ratio, generated voltage, alternator speed and failure information from the alternator through a communication line, and a malfunction judging unit judging, from the battery current, the battery voltage, the battery temperature and the conditions of the alternator, whether or not a malfunction has occurred in one of the alternator, the battery and the detecting units. In response to the judgment that a malfunction has occurred in one of the alternator, the battery and the detecting units, a notifying unit notifies the occurrence of the malfunction.