Battery monitoring device

A battery monitoring device for monitoring a state of a rechargeable battery that includes an electrolyte and a plurality of electrodes, comprising:

• a signal control unit configured to instruct emission of a predefined AC signal;
• a response signal input unit configured to receive a response signal of the rechargeable battery to the AC signal;
• a calculation unit configured to calculate a complex impedance of the rechargeable battery based on the response signal;
• and
• a power supply unit configured to receive a power supply voltage from the rechargeable battery and supplies the power supply voltage to at least the calculation unit,
• wherein 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, and
• the signal control unit is configured to cause the rechargeable battery to be monitored, as a power source, to output the predefined AC signal.