Definition
An electrical state in which the aircraft battery is supplying current to the electrical system without being replenished by the alternator or generator, resulting in a net loss of stored energy over time. On the ammeter, this is shown as a negative reading, indicating current is flowing out of the battery rather than into it.
Plain English
The battery is being drained because nothing is recharging it. Power is going out of the battery faster than it is coming in, so the battery is slowly running down.
Context Anchor
Seen during alternator or generator failure checks, usually through an electrical gauge, a voltage indication, or an electrical warning light.
Derivation
Discharge' comes from Old French 'descharger,' meaning to unload or release. In electrical use, it describes a battery releasing its stored energy. A discharge condition is simply the state of that unloading happening in flight.
Why Pilots Care
A discharge condition signals that battery power is being consumed and will eventually be exhausted, leading to loss of electrically powered instruments, radios, and navigation equipment if loads are not reduced.
Analogy
It is like using a phone while it is not charging: the phone may still work for a while, but the battery level keeps going down.
Intuition Check
Do not read discharge here as simply “letting something out” in a general sense. In this context, it means the aircraft battery is losing stored electrical energy because it is powering the system.
Example Sentence 1
After the alternator failed, the ammeter showed a discharge condition, so the pilot turned off non-essential electrical equipment to extend battery life.
Example Sentence 2
Continued flight with an unresolved discharge condition will deplete the battery and leave the aircraft without power for critical instruments.