A backup power supply is provided. The backup power supply provides batteries electrically coupled to a power cord for receiving power for charging the batteries and a power outlet for transmitting power for powering electrical equipment coupled to the power outlet. An inverter generator is operatively associated with the power cord, the batteries, and the power outlet in such a way that when the power cord experiences an electrical short the batteries switch from a reserve mode receiving power to a backup mode for transmitting power to the power outlet. The invertor generator is also adapted to sense reception of power through the power cord so as to switch from the backup mode to the reserve mode. Visible and audible indicators are provided for indicating the switching between the reserve mode and the backup mode.