Abstract: A battery backup unit (BBU) includes a housing, at least one battery compartment in the housing with an output terminal, a DC input, a DC output, a path from the DC input to the DC output, circuitry for selectively connecting the output terminal to the path, which circuitry includes a switch, and a controller configured to detect a condition of the path and selectively control the switch to connect the output terminal to the path when the condition is detected, the BBU being incapable of charging batteries in the at least one battery compartment. The path from the DC input to the DC output may include a DC/DC step up converter to help maintain a constant output voltage.