Final answer:
The emergency power in a helicopter's electrical system, as suggested by the question, is set to last either 12 hours at full power or 24 hours at half-power. This ensures critical systems remain operational during emergencies. The battery charging is maintained through the 'STBY BATT' circuit breaker.
Step-by-step explanation:
The student's question pertains to the duration that emergency power is provided by the onboard battery in a helicopter's electrical system. According to the information implied in the question, we can deduce that the emergency power has a minimum duration. If we assume that emergency power can be sustained only on for 12 hours, or alternatively, capable of operating at half-power for 24 hours, we can conclude that the emergency power supply is designed for a time span that could either be continuous full power for half a day or a reduced power mode that lasts for a full day.
This duration of power supply assures that critical avionics and navigation systems continue to operate in the event of a failure in the primary electrical system, until an appropriate safety measure such as an emergency landing can be executed. The battery itself is maintained through the 'STBY BATT' circuit breaker, which ensures it is regularly charged while the helicopter's main electrical system is operational. This safety measure is critical for helicopter operations, especially during emergencies when the reliable functionality of the helicopter's systems is paramount.