46 CFR 113.10-9: -9 Power supply.

(a) General. There must be at least two sources of power for the electrical equipment of each fire detecting and alarm system. The normal source must be the main power source. The other source must be the emergency power source or an automatically charged battery. If the other source is an automatically charged battery, the charger must be supplied from the final emergency power source. Upon loss of power to the system from the normal source, the system must be automatically supplied from the other source.

(b) Batteries. Each battery used in a fire detecting and alarm system must meet Subpart 111.15 of this chapter.

(c) Capacity of power supply branch circuit. The capacity of each branch circuit providing power to a fire detection or alarm system must not be less than 125 percent of the maximum load.