A battery monitoring apparatus capable of reducing power consumption. At least one monitoring integrated circuit (IC) is electrically connected to a high-voltage battery formed of a plurality of cells and configured to monitor the high-voltage battery in a plurality of modes of operation. A low-voltage power supply circuit can deliver power of a lower voltage than the power of the high-voltage battery to the at least one monitoring IC. A power supply to the at least one monitoring IC is selected from a group of the high-voltage battery and the low-voltage power supply circuit depending on the mode of operation the at least one monitoring IC.