Patent ID: 7847558

Claim:
A battery system, comprising: a battery having a first plurality of cells electrically coupled in series to one another between a first battery terminal and a second battery terminal, the first plurality of cells comprising a second plurality of cells and a third plurality of cells coupled together at a node, each cell of the first plurality of cells having a desired output voltage level during desired operation; and a battery monitor electrically coupled to the battery at the node and at the first and second battery terminals, the battery monitor configured to measure a first voltage level of the first plurality of cells of the battery when the first plurality of cells are not coupled to a load, the battery monitor further configured to measure a second voltage level at the node between the second plurality of cells and the third plurality of cells when the first plurality of cells are coupled to the load, the battery monitor further configured to calculate a first number of failed cells of the first plurality of cells based on the first voltage level, the desired output voltage level of each cell of the first plurality of cells and a number of cells in the first plurality of cells, the battery monitor further configured to calculate a second number of failed cells of the second plurality of cells based on the second voltage level, the desired output voltage level of each cell of the first plurality of cells and the first number of failed cells, and the battery monitor further configured to calculate a third number of failed cells of the third plurality of cells based on the second voltage level, the desired output voltage level of each cell of the first plurality of cells and the first number of failed cells.