A modular case having similarly sized U-shaped sections that enclose energy storage cells and a battery management system. Additional modules can be ganged together to increase the energy storage and output capacity. Removable panels in the sections can be removed for the installation of jacks and a status display. Various charging sources can be coupled to the module including solar, generator and AC mains for charging. An output switch selectively delivers AC mains power when available, and then switches to battery power during periods of AC mains unavailability.