First appears in: The Metal Wood
Power Storage Seven is a "sabotaged power facility" described as a "chamber... extremely tall, maybe a hundred feet at least, filled with great long cylindrical things that functioned as giant batteries". The facility is linked to the city's secret "underroad," which transitions into "thick metal grating" as it passes through the center of the storage room.
The location was the site of a massive, mysterious fire that "managed to destroy the entire local electric system and all its backup power". The incident was particularly significant because the "power cells are not flammable," leading the Den Boss to realize the fire was an act of "wanton destruction" intended to destabilize the city. Phoenix was "almost destroyed" when she drove into the chamber and found the massive batteries "completely covered in flames".