Patent ID: 8178227

Claim:
A method of detecting and responding to a cell failure of at least one cell of a plurality of cells comprising a battery pack, the method comprising the steps of: periodically monitoring an electrical isolation resistance of said battery pack; comparing said electrical isolation resistance to a first preset resistance value; determining when said electrical isolation resistance falls below said first preset resistance value; determining when said electrical isolation resistance recovers to greater than a second preset resistance value, wherein said step of determining when said electrical isolation resistance recovers to greater than said second preset resistance value is performed after said electrical isolation resistance is determined to have fallen below said first preset resistance value; determining a time period from a first time when said electrical isolation resistance is determined to have fallen below said first preset resistance value to a second time when said electrical isolation resistance is determined to have recovered to greater than said second preset resistance value; determining if said time period is within a preset time range; determining when said electrical isolation resistance falls below a third preset resistance value, wherein said step of determining when said electrical isolation resistance falls below said third preset resistance value is performed after said electrical isolation resistance recovers to greater than said second preset resistance value; and performing a predetermined cell failure response after said electrical isolation resistance falls below said first preset resistance value and recovers to greater than said second resistance value and then falls below said third preset resistance value and if said time period is within than said preset time range.