Definition
A chemical cell that produces electrical energy through an irreversible chemical reaction. Once the active chemicals inside are consumed, the cell cannot be returned to its original state by passing current through it in reverse, so it must be discarded when discharged.
Plain English
A battery cell that can be used until it goes flat, but cannot be recharged. When it stops producing power, it is thrown away and replaced.
Context Anchor
Seen in aircraft electrical system discussions, battery descriptions, emergency equipment, and maintenance instructions for battery-powered devices.
Derivation
From Latin primarius, meaning 'first' or 'original.' The name reflects that the cell produces electricity directly from its first and only chemical reaction, with no second life through recharging.
Why Pilots Care
Knowing whether a battery is a primary cell or a secondary (rechargeable) cell determines how it is maintained and replaced. ELT batteries, for example, are typically primary cells with a fixed replacement schedule, and using the wrong type can render safety equipment inoperative.
Intuition Check
“Primary” does not mean the airplane’s main battery here. It means a non-rechargeable cell. “Cell” does not mean a phone or prison room here. It means one small unit that produces electricity.
Example Sentence 1
The emergency locator transmitter uses primary cells, so the entire battery pack must be replaced on its scheduled date rather than recharged.
Example Sentence 2
During preflight the mechanic replaced the primary cells in the flashlight kept in the cockpit.