A battery monitoring apparatus comprises a reception section to receive a radio signal and to output power and a demodulated signal according to the radio signal; a first power source circuit to perform power supply based on the power; a decode circuit to operate upon receiving the power supply from the first power source circuit and to output an activation signal and a command based on the demodulated signal; a second power source circuit to be activated according to the activation signal and to perform power supply; a battery monitoring circuit to operate upon receiving the power supply from the second power source circuit and to output a monitoring result of a state of the battery according to the command; and a transmission section to operate upon receiving the power supply from the second power source circuit and to wirelessly transmit the monitoring result.