Definition
A method of charging a storage battery in which the charging source is held at a fixed voltage slightly higher than the battery's nominal voltage. Current flows into the battery at a high rate when it is deeply discharged and tapers off automatically as the battery's voltage rises toward the source voltage. This is the standard charging method used in aircraft electrical systems, where the generator or alternator and its voltage regulator hold bus voltage constant.
Plain English
A way of charging a battery by keeping the charging voltage fixed. The battery pulls a lot of current when it is low and gradually pulls less as it fills up, until it stops drawing current on its own.
Context Anchor
Seen in aircraft battery maintenance, electrical system servicing, and battery charger instructions.
Derivation
"Constant" means unchanging, and "voltage" is the electrical pressure pushing current through a circuit. So a constant-voltage charge is exactly what it says: the voltage stays the same while the current is allowed to vary.
Why Pilots Care
Proper constant-voltage charging prevents overcharging, extends battery life, and maintains reliable electrical power for engine starting and avionics.
Analogy
Like filling a water tank from a hose at fixed pressure: flow is strong when empty and slows as the tank nears full.
Intuition Check
Do not read “constant-voltage” as meaning the whole charging process stays constant. The voltage stays fixed; the amount of electricity flowing into the battery changes.
Example Sentence 1
The aircraft's voltage regulator provides a constant-voltage charge to the battery whenever the engine is running.
Example Sentence 2
After a constant-voltage charge cycle the battery was reinstalled and passed the capacity test without issue.