Abstract: According to the present invention, an emergency power supply to be coupled to an electric power source providing an incoming AC signal may include an input/output terminal, a battery with a DC voltage, a rectifier coupled directly to the input/output terminal and connected to the battery, an inverter coupled directly to the input/output terminal and connected to the battery, and a control circuit coupled to the rectifier and the inverter so that in a first operational mode the rectifier is coupled to the battery to rectify an incoming AC signal at the input/output terminal to charge the battery and the inverter is decoupled from the battery, and in a second operational mode the inverter is coupled to the battery to invert the DC voltage to provide an outgoing AC signal at the input/output terminal and the rectifier is decoupled from the battery.