What is the meaning of "Reserve Source of Energy"?

High caloric value items for lifeboat, per SOLAS regulations.

Diesel fuel stored for the purpose of operating the powered survival craft for a period equal to or exceeding the U.S.C.G. and SOLAS requirements.

Power to operate the radio installation and conduct Distress and Safety communications in the event of failure of the ship's main and emergency sources of electrical power.

The diesel fueled emergency generator that supplies AC to the vessel's Emergency power bus.

What is the meaning of "Reserve Source of...