In many countries the underdeveloped electricity grid does not only affect the people that are not connected to the grid. Also those that are connected often suffer due to power cuts that can last from some seconds to several days. For those who need a reliable power supply, back-up systems can be individually designed. The back-up system contains an inverter/charger and battery packs to store the energy. It can be exclusively served by the grid, or can be supported by an additional source of energy like a Photovoltaic or hybrid system.