Patent ID: 8643332

Claim:
A battery system, comprising: a battery pack that includes parallel battery units, each of the parallel battery units including a plurality of battery cells connected to each other in parallel, and the plurality of parallel battery units being serially connected to each other to form the battery pack; a storage portion that stores reference data regarding a relationship between reference voltage values and accumulated current values, the reference data being previously obtained based on measured experimental results and the accumulated current values being current integrated values; a detecting portion that detects voltage and current of each of the parallel battery units, and calculates an accumulated current value of each of the parallel battery units based on the detected current of each of the parallel battery units; a determining portion that reads, from the reference data in the storage portion, one of the reference voltage values corresponding to the accumulated current value of each of the parallel battery units detected by the detecting portion, and compares the read reference voltage value with the detection voltage of each of the parallel battery units detected by the detecting portion, wherein the determining portion is configured to determine that the parallel battery unit includes a battery cell where an internal short circuit occurs if a difference between the read reference voltage value and the detection voltage of the parallel battery unit is larger than a predetermined value.