BATTERY MONITORING DEVICE

In a battery monitoring device for monitoring a state of a rechargeable battery that includes an electrolyte and a plurality of electrodes, a response signal input unit is configured to receive a response signal of the rechargeable battery to a predefined AC signal, and a calculation unit is configured to calculate a complex impedance of the rechargeable battery based on the response signal. A power supply unit is configured to receive a power supply voltage from the rechargeable battery and supplies the power supply voltage to at least the calculation unit. A first electrical path connecting the rechargeable battery to the power supply unit and a second electrical path connecting the rechargeable battery to the signal control unit are provided independent of each other. The signal control unit is configured to cause the rechargeable battery to be monitored, as a power source, to output the predefined AC signal.