Maintaining operations in the event of a complete power outage requires a tested and established:

A hardware maintenance plan addresses scheduled upkeep and repair of physical equipment, not the continuation of operations during an unplanned outage.

A site recovery plan focuses on restoring IT infrastructure and facilities after a disaster, which is a subset of continuity planning and does not cover the full scope of keeping operations running.

A business continuity plan (BCP) documents the processes, resources, and procedures required to keep critical operations running during and after a disaster such as a complete power outage. It is broader than IT recovery alone and must be tested and established before an incident to be effective, which aligns exactly with the requirement stated in the question.

An incident response plan governs the detection, containment, and remediation of security incidents and does not address operational continuity during power or infrastructure failures.