Battery sensor and battery monitoring system

A battery monitoring system which monitors a first battery and a second battery connected to a negative electrode of the first battery in series, the system comprising:

• an ammeter resistor connected in series between the negative electrode of the first battery and a positive electrode of the second battery;
• a first integrated circuit configured to detect a first battery voltage outputted from the positive electrode of the first battery, a one-directional current of the first and second batteries, and a temperature of the first battery;
• a second integrated circuit configured to detect a voltage of the second battery and a temperature of the second battery;
• a master ECU connected to the second integrated circuit through a vehicle network and configured to receive the first battery voltage, the second battery voltage, the one-directional current of the first and second batteries, and the temperatures of the first and second batteries through the vehicle network, and control charging of the first and second batteries and confirm whether the first and second batteries have a problem based on the received first battery voltage, second battery voltage, one-directional current of the first and second batteries, and temperatures of the first and second batteries;
• and
• a serial communication interface for communication connection between the first integrated circuit and the second integrated circuit,
• wherein the serial communication interface includes an isolator configured to permit a signal transmission in a forward direction from the first integrated circuit to the second integrated circuit and block a signal transmission in a backward direction from the second integrated circuit to the first integrated circuit.