Electric vehicle battery pack voltage monitoring

Total voltage output by a multi-cell battery pack in an electric vehicle is monitored. A main microcontroller having a chassis ground is digitally isolated from positive and negative busses of the battery pack. A battery monitoring IC having a plurality of auxiliary/thermistor A/D inputs measures respective voltages of the battery cells. A voltage divider is selectably coupled to the positive bus by an evaluation switch under control of the main microprocessor with an auxiliary output terminal of the IC. A divided voltage is coupled to one of the auxiliary/thermistor A/D inputs. The battery monitoring IC transmits a digital value representative of the divided voltage output to the main microprocessor via the serial data link, and the main microprocessor determines the main battery voltage in response to the digital value.