What is the meaning of “Reserve Source of Energy”?

The supply of electrical energy sufficient to operate the radio installations for the purpose of conducting Distress and Safety communications in the event of failure of the ship’s main and emergency sources of electrical power.

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.