How many minutes of emergency DC power does the battery provide at 80% charge?

The correct answer indicates that at 80% charge, the battery is capable of providing 20 minutes of emergency DC power. This duration is significant because it reflects the battery's design to supply critical electrical power during emergencies when the primary power source is lost or fails. In the context of aircraft operations, sufficient backup power is vital for maintaining control and functionality of essential systems.

The battery's capacity to sustain a 20-minute supply at this charge level is based on the system's requirements and operational safety measures. It is often engineered to ensure that the aircraft can maintain basic systems like communication, navigation, and flight instrumentation, thus allowing for safe management of emergencies until the primary power can be restored or the aircraft can be landed safely.

Other potential answer choices would imply shorter durations, which would not provide adequate time for emergency procedures and could compromise safety. Hence, the design specifications emphasize the need for a reliable power source that meets operational demands, confirming the choice of 20 minutes as the correct answer.