Definition
The length of time an aircraft battery can supply electrical power to essential systems before its voltage drops below a usable level. In the context of alternator or generator failure, it refers specifically to the limited period during which the battery alone can power required equipment such as radios, flight instruments, and lighting after the primary electrical generation source is lost.
Plain English
How long the battery can keep things running on its own after the alternator or generator quits. Once the battery runs down, the equipment it was powering goes dark.
Context Anchor
Used in discussions of alternator or generator failure, when the aircraft may be running on battery power alone.
Derivation
Battery comes from an older word for a group of things working together; an electrical battery is a group of cells that store power. Life means the useful working period of something. In this context, battery life means the useful time left before the battery can no longer power what the pilot needs.
Why Pilots Care
It shows how much time remains to reach an airport or restore power before critical systems are lost.
Analogy
It is like a phone battery during a power outage: the more features you leave on, the faster the remaining time disappears.
Intuition Check
Do not read battery life here as the age of the battery or how many years it will last. In this situation, it means the time left before the battery’s stored power is used up.
Example Sentence 1
After the alternator failed, the pilot turned off non-essential equipment to extend battery life long enough to reach the nearest airport.
Example Sentence 2
With reduced battery life only the navigation and communication radios stayed powered on.