Definition
A unit of electrical capacity equal to a current of one ampere flowing for one hour. It expresses how much electrical charge a battery can deliver before being fully discharged. A battery rated at 35 ampere-hours can theoretically supply 35 amperes for one hour, or 1 ampere for 35 hours.
Plain English
A measure of how much electricity a battery can store. The bigger the number, the longer the battery can keep things running before it goes flat.
Context Anchor
Seen in aircraft battery ratings, electrical-system discussions, maintenance records, and emergency planning for battery-only operation.
Derivation
A combination of two units: ampere (the unit of electric current, named after French physicist André-Marie Ampère) and hour. Multiplying current by time gives total charge delivered, which is what the term measures.
Why Pilots Care
Battery ampere-hour ratings indicate how long essential electrical systems can operate if the alternator fails.
Analogy
Think of it like the size of a fuel tank, but for stored electricity. A larger ampere-hour rating usually means more stored electrical capacity, though the actual usable time still depends on how much equipment is drawing power.
Intuition Check
Do not read ampere-hour as “the number of hours the battery will last.” It is current multiplied by time, so actual battery time depends on electrical load, battery condition, temperature, and the battery’s state of charge.
Example Sentence 1
The aircraft's battery is rated at 25 ampere-hours, giving roughly 30 minutes of essential bus power if the alternator fails.
Example Sentence 2
With the alternator offline, the pilot knew the 35 ampere-hour battery would keep the essential bus powered for several hours.