47 C.F.R. § 80.965 – Reserve power supply.

(a) Each passenger vessel of more than 100 gross tons and each cargo vessel of more than 300 gross tons must be provided with a reserve power supply independent of the vessel's normal electrical system and capable of energizing the radiotelephone installation and illuminating the operating controls at the principal operating position for at least 2 continuous hours under normal operating conditions. When meeting this 2-hour requirement, such reserve power supply must be located on the bridge level or at least one deck above the vessel's main deck.
(b) Instead of the independent power supply specified in paragraph (a) of this section, the vessel may be provided with an auxiliary radiotelephone installation having a power source independent of the vessel's normal electrical system. Any such installation must comply with §§ 80.955, 80.956, 80.957, 80.959, 80.961, 80.969 and 80.971, as well as the general technical standards contained in this part. Additionally, the power supply for any such auxiliary radiotelephone must be a “reserve power supply” for the purposes of paragraphs (c), (d) and (e) of this section.
(c) Means must be provided for adequately charging any batteries used as a reserve power supply for the required radiotelephone installation. A device must be provided which, during charging of the batteries, gives a continuous indication of charging.
(d) The reserve power supply must be available within one minute.
(e) The station licensee, when directed by the Commission, must prove by demonstration as prescribed in paragraphs (e)(1), (2), (3), and (4) of this section that the reserve power supply is capable of meeting the requirements of paragraph (a) of this section as follows:
1. (1) When the reserve power supply includes a battery, proof of the ability of the battery to operate continuously for the required time must be established by a discharge test over the required time, when supplying power at the voltage required for normal operation to an electric load as prescribed by paragraph (e)(3) of this section.
2. (2) When the reserve power supply includes an engine driven generator, proof of the adequacy of the engine fuel supply to operate the unit continuously for the required time may be established by using as a basis the fuel consumption during a continuous period of one hour when supplying power, at the voltage required for normal operation, to an electrical load as prescribed by paragraph (e)(3) of this section.
3. (3) For the purposes of determining the electrical load to be supplied, the following formula must be used:
  1. (i) One-half of the current of the radiotelephone while transmitting at its rated output, plus one-half the current while not transmitting; plus
  2. (ii) Current of the required receiver; plus
  3. (iii) Current of the source of illumination provided for the operating controls prescribed by § 80.969; plus
  4. (iv) The sum of the currents of all other loads to which the reserve power supply may provide power in time of emergency or distress.
4. (4) At the conclusion of the test specified in paragraphs (e)(1) and (2) of this section, no part of the reserve power supply must have excessive temperature rise, nor must the specific gravity or voltage of any battery be below the 90 percent discharge point.