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Battery cell operating characteristics were determined for a unique load profile planned for the Motorola Iridium™ spacecraft. The Iridium™ mission requires that the battery be on line at all times and operated for extended periods with a short duration, high rate, charge/discharge duty cycle. The effort reported here reflects a repetitive duty cycle of 1.3 milliseconds discharge and 2.9 milliseconds charge, with discharge rates in the range 2.0 C to 3.0 C and charge rates in the range 0.9 C to 1.4 C. Cell transient characteristics were determined for candidate cell types including nickel-hydrogen individual pressure vessel (IPV), nickel-hydrogen common pressure vessel (CPV), Super nickel-cadmium, and fiber nickel-cadmium (FNC). Experimental approach, cell performance data, derived transient characteristics, and cell electrical models are presented.