Abstract: A circuit 10 has a high voltage battery 12 that includes a first battery portion V1, a second battery portion V2, and a third battery portion V3. Each of the three battery portions is coupled in series to form the high voltage battery 12. A controller 52 includes a pulse width modulated controller 56 and a voltage sense and comparator circuit 54. Each of the terminals of the battery portions are coupled to a respective switch. By sensing the voltages at the respective terminals, the state of charge of each of the battery portions is determined. The battery portions having the highest state of charge are used to charge the low voltage battery and/or operate the load 50. The controller controls the operation of the switches to provide connections of the battery portions V1-V3 to the load.

Abstract: In one embodiment of the present invention, a system is provided or measuring the voltages of the traction batteries of an electric vehicle. The system includes switches provided to switchably couple the batteries individually to an amplifier. The system also includes switches provided to assure that the same polarity is always provided to the amplifier; a single-ended amplifier can thus be used. The system includes an analog-to-digital converter coupled in communication with the output of the amplifier, and an optical coupler which couples the output of the analog-to-digital converter to the low-voltage portion of the electric vehicle's electrical system.