Definition
A secondary, independent battery installed in some aircraft to provide backup electrical power to essential flight instruments and avionics if the main battery and generator/alternator both fail. In glass-cockpit aircraft, the standby battery typically powers a reduced set of critical displays and the attitude indicator long enough to complete an approach and landing.
Plain English
A backup battery that keeps your most important flight instruments running if the normal electrical system quits.
Context Anchor
Seen on cockpit displays, system diagrams, warning messages, and checklist items related to electrical power problems.
Derivation
"Standby" comes from the idea of something held in reserve, ready to step in. The standby battery sits unused during normal flight and only takes over when the primary electrical system fails.
Why Pilots Care
Maintains attitude reference, navigation, and communication capability during electrical emergencies to prevent loss of control in instrument conditions.
Intuition Check
Standby does not mean unimportant or optional here. It means held in reserve and ready to supply backup power when normal power is lost.
Example Sentence 1
After the alternator failed, the pilot turned on the STBY BATT to keep the primary flight display powered for the diversion.
Example Sentence 2
The preflight check confirmed that STBY BATT voltage was within limits before departure into IMC.