Batteries for the storage of electrical energy are known in the art. They are used in a wide variety of applications. The applications vary from space satellites, which usually will represent relatively small energy storage requirements, through electric vehicles which represent energy storage at the 50 kilowatt-hour level, to electric utility load leveling batteries which will require 100 megawatt-hour levels of energy storage. The number of cells associated with a battery may vary from 10 to over 2,000,000. As the complexity of a battery increases, it is increasingly necessary to provide means for locating and isolating a failed cell within the battery. Otherwise, a failed cell can deplete energy from good cells or actually cause physical damage to good cells.
The network of cells in a battery may be connected in series or in parallel. A failed or failing cell has a substantially adverse impact on the remaining good cells. For cells in parallel, a cell which has failed in such a manner as to create a short-circuit can drain the capacity of all of its parallel network members. Similarly, for cells in series, a cell which has failed in such a manner as to become non-conductive, or to become an open-circuit, removes from access the capacity of its undamaged series members. The failed cell problem is compounded by the fact that cells generally fail in a random manner, thus preventing any solution based upon a predicted location of a failed cell or the predicted kind of failure of the cell.
In the prior art, these problems have been addressed through the utilization of fuses. The successful use of fuses requires excess current flow through the cell as a result of cell failure. The excess current must be sufficient to melt the fusible link of the fuse. This approach is unreliable since a failed cell need not result in current of sufficient magnitude to cause the desired fusing action.