Satellite electrical power systems (SEPS) are strongly interdisciplinary, exhibit complex nonlinear behavior, and operate over a wide range of power levels. The Virtual Test Bed (VTB) provides a unified computational environment that allows rapid modeling, simulation and virtual-prototyping of such complex systems. VTB handles modeling in a comprehensive and efficient way by using both topological and mathematical descriptions. The VTB is also endowed with mechanisms to import models and to co-simulate with other standard software. This paper presents a study of two representative SEPSs to demonstrate design and testing of such systems in the VTB. The performances of Li-ion and Ni-H-2 batteries are compared in a particular system. (C) 2003 Elsevier Science B.V. All rights reserved.