Battery Management Systems (BMS) using Li-Ion batteries are driving toward the ability to measure voltage and current at ever tighter tolerances. The more accurate the measurement, the more accurate the State of Charge (SoC) or in the case of an Electric Vehicle Distance to Empty (DTE). This has pushed differential cell voltage measurement accuracy requirements down to 100uV in a 5V range. The QMS has excellent resolution and accuracy but needs to be tighter for future BMS test requirements. The goal is to reduce the offset and gain errors of the QMS allowing for a ±100uV or better short-term measurement accuracy. This presentation will detail the methods used on the ETS-800 to improve its short-term accuracy, including evaluating a reduction in the specified temperature range of ±5֩C and enabling an Auto-Cal procedure for the QMS when its temperature drifts from a specified limit. We’ll also discuss how the QMS’s 5V measurement accuracy will be verified using a High Precision Voltage Reference ±(0.3 uV/V at 30 days), Noise ±(0.06 uV/V rms) and Temperature Coefficient ±(0.04 uV/V per ֩C).