Which power failure does the battery support with emergency power?

The battery primarily supports DC power failure with emergency power. In aviation systems, batteries are primarily designed to supply direct current (DC) to critical systems when the standard power sources are unavailable. This is essential for maintaining operations of vital instruments, communication systems, and navigational aids during an unexpected loss of standard power sources.

It's important to understand that while batteries can contribute to some essential functions in various power failure scenarios, they are specifically tailored to address the needs associated with DC power loss. This is primarily due to the fact that many onboard systems operate on a DC architecture, and the battery is equipped to ensure continued functionality during such an outage.

In contrast, AC power failures would typically rely on different backup sources like generators, and emergency or backup power failures do not describe a specific type of electrical power loss but rather imply a lack of overall power redundancy.