NOVELTY - The pack has two housings which are affixed together. Several battery cells (102) engaging and residing within housings, are not movable with respect to housings. A lattice structure of battery cell supports are located in the housing. A variable bias device is engaged in lattice structure. The variable bias device is engaged by printed circuit board resides in lattice structure. Several fixed mechanically biased electrical contact devices are affixed to the circuit board. Several fixed bias contact devices are interposed between circuit board and battery cells.    USE - Fail-safe battery pack in the field of intelligent power supply management system for battery electric vehicle (BEV) such as car, truck, and military vehicle. Can also be used in hybrid electric vehicle (HEV), plug-in HEV (PHEV), fuel cell electric vehicle (FCEV), homeland defense, military, industrial, and residential regions.    ADVANTAGE - The failed cells are easily removed and replaced with appropriate cells due to the ability of identifying a failed or failing cell or cells within a battery pack for returning the battery pack to service, so that the high value of the intact components of the battery pack is preserved. The battery pack is able to transform itself from an efficient, high-voltage configuration while operating a load under normal conditions to a low-voltage. Thus the safe configuration whenever desired such as periods of general inactivity, handling by humans or machines, shipping, or abnormal conditions such as accidents or malfunctions is achieved. The modular pack is quickly exchanged by either man or machine with enhanced serviceability and maintenance. The cost, power, range, and weight of modular packs are reduced, so that the life extension and temperature management is improved. The roadside emergency efficiency of the pack is increased. The service time of the pack is reduced due to the presence of hierarchical drawers. Energy accounting, safety, and shipping efficiency is improved.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method for operating fail-safe battery pack.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of the intelligent power supply device.    Battery cells (102)    Shelves (103)    Door (107)    Button (111)    Spring tongue (112)