A battery monitor system for determining a cell voltage between a low side contact and a high side contact of a cell in situ as one of a plurality of cells connected in series to form a battery. The system uses an arrangement of switches and capacitors to shift relatively high absolute voltages of a battery stack to a relative low voltage level so lower voltage electronics can be used to monitor cell voltages. The system may be configured to provide a single ended measurement or a differential measurement indicative of a cell voltage. The differential measurement may be advantageous to correct or offset signal noise caused by electromagnetic interference (EMI).