The design, analysis, and testing of a multi-module, multi-phase (MMMP) battery charger for the NASA Earth Observing System (EOS) is presented. The MMMP converter is comprised of four independent buck converters switched 90° out of phase. The MMMP charger is compared to a single module battery charger, and shown to provide significant performance improvements. The power stage is designed for maximum efficiency and minimum weight. The control loops (Charge Regulation and Bus Voltage Regulation) designs are presented and the small-signal models are verified with experimental results. The charger testing is facilitated by the use of the Space Platform Power System Hardware Testbed. The testbed utilizes battery and solar array simulators which allow for realistic battery charger testing. / Master of Science