Both the E-3 Centurion AWACS and E-6 Mercury TACAMO Aircraft have identical airborne battery and charger systems. High maintenance costs due to high failure rates of the battery components prompted NAVAIR to begin a program to replace the commercial battery with a high-reliability military specification battery. The new design, specified as the M81757/18-1, uses modern materials and low-maintenance vented nickel-cadmium (Ni-Cd) technology. The prototype batteries were developed by MarathonNorco Aerospace Inc. Realizing that the charge algorithm of the present airborne charger was a very mild charge for a 20-cell, nickel-cadmium (Ni-Cd) battery, prototypes of the new batteries were tested to verify whether the airborne chargers could keep them adequately charged. The present airborne charger could not keep the new batteries charged. The initial plan to insert the new technology battery into the existing airborne system would not work without changing the present airborne charger. Although the charge algorithm was a very gentle charge, there were reports about the present batteries overheating on the aircraft. The empirical evidence appeared to strongly contradict all operating descriptions of the airborne charger. To understand the reason for the apparent contradiction between the system operating description and actual occurrences, we began to study the airborne charge system. The more we learned, the more we realized that the whole system should be replaced.
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