The aim of this paper is to describe the JASON 1 electrical power subsystem (EPS) and the associated validation method. JASON 1 EPS is based on an unregulated bus. On Board Software can connect and disconnect solar array sections to the satellite power bus according to instantaneous satellite needs. The EPS concept has been validated with simulation means based on the Saber® software. Saber® has a modeling language capable of reproducing the On-Board Software (OBS) battery management application as well as the behavior of the EPS equipment. A Tcl/Tk tool permitted to optimize the OBS parameters dedicated to the battery management and to check the EPS robustness.