Automobiles, aircraft, marine vehicles, uninterruptiblepower supplies and telecom hardware represent areasutilizing series connected battery stacks. These stacksof individual cells may contain many units, reaching potentialsof hundreds of volts. In such systems it is oftendesirable to accurately determine each individual cell’svoltage. Obtaining this information in the presence of thehigh “common mode” voltage generated by the batterystack is more diffi cult than might be supposed.