A battery monitoring system includes battery measuring devices and a battery monitoring device. Each of the battery measuring devices detects voltage information on a corresponding battery. The battery monitoring device is configured to: acquire the voltage information from each of the battery measuring devices by using wireless communication; and acquire current information on current flowing through the corresponding battery from an electric-current sensor. The battery monitoring device includes a control unit and a wireless communication unit. The wireless communication unit executes wireless communication with the battery measuring devices with a predetermined period. The control unit is configured to: cause the wireless communication unit to output a voltage measuring instruction; and based on a timing at which the wireless communication unit transmits the voltage measuring instruction to the battery measuring device, acquire the current information during a time interval in which the battery measuring device acquires voltage information.