Battery monitoring device and battery system monitoring device

A battery monitoring device for monitoring a cell group made by connecting a plurality of single battery cells in series, comprising:

• a first switching circuit configured to select, as a measurement target voltage, any one of a plurality of types of voltages including the cell voltages of the single battery cells in the cell group;
• a differential amplifier circuit including a first input terminal and a second input terminal, and configured to convert the measurement target voltage, which is selected by the first switching circuit and input to between the first input terminal and the second input terminal, into a voltage in a predetermined range by performing differential amplification;
• an AD converter configured to measure the measurement target voltage which is selected by the first switching circuit and converted by the differential amplifier circuit, and output a digital signal according to the measurement result;
• and
• a first voltage reference connected to a positive electrode-side or a negative electrode-side of a single battery cell of the single battery cells of the cell group except the negative electrode-side of the single battery cell of the lowest potential in the cell group, and configured to generate
• a first reference voltage using the potential of the positive electrode-side or the negative electrode-side of the single battery cell as a reference,
• wherein by causing the first switching circuit to select the first reference voltage, the first reference voltage converted by the differential amplifier circuit is output to the AD converter as an abnormality detection voltage, with which abnormality in a differential amplification characteristic of the differential amplifier circuit is detected.