US Patent 9140761 Battery pack failure detection device

Each detection unit is configured to compare a voltage output from a battery cell associated therewith a predetermined criterion voltage. A plurality of detection units operate sequentially in response to a start trigger and also sequentially transmit a signal that reflects a result of comparing the voltages to detect whether a battery pack has a low cell voltage fault. A fault monitoring device detects an internal resistance fault when it receives from a transmission circuit a determination signal indicating that the battery pack when electrically discharged has any of its battery cells outputting a voltage decreased to be lower than the criterion voltage and if a current detected has a value smaller in magnitude than a criterion current corresponding to a value of a current obtained by dividing a difference in voltage between an open circuit voltage of the battery cell and the criterion voltage by an upper limit value for internal resistance.