Under normal circumstances it is powered with network voltage via a load transformer. At the same time a bidirectional converter is powered via the other winding of the transformer. This way the transformer acts as a rectifier or a charger that charges the battery group. When the mains voltage is interrupted or out of tolerance the static toggle switch opens and the inverter starts operating as converter in order to feed the load. The battery inverter duo will ensure the continuity of energy until the stored energy runs out or the AC mains return into the tolerance.