In SEPAC Project which was performed in Space Shuttle Spacelab-1 in 1983 to conduct active experiments in space, a battery power supply for the Electron Beam Accelerator was used. It was a power supply composed of high voltage (450 V), high duty (15 CA), 4Ah sealed type Ni-Cd battery package. This is to report on its requirement, development history, specification (structual and electrical characteristics), test procedure and results and the performance on the Space Shuttle.