Definition
A rechargeable secondary-cell battery that uses nickel hydroxide as the positive plate material, cadmium hydroxide as the negative plate material, and potassium hydroxide as the electrolyte. Unlike a lead-acid battery, the electrolyte does not chemically react with the plates and its specific gravity does not change with state of charge, so charge level cannot be measured with a hydrometer. Nickel-cadmium batteries hold a steady output voltage through most of their discharge cycle and can deliver very high current, but are prone to thermal runaway if overcharged.
Plain English
A rechargeable aircraft battery that uses nickel and cadmium plates instead of lead. It holds a steady voltage almost until it's empty, can put out a lot of power quickly, and needs careful charging to keep from overheating.
Context Anchor
Pilots encounter nickel-cadmium batteries in aircraft electrical system descriptions, maintenance records, emergency power discussions, and some preflight or abnormal procedure guidance.
Derivation
Named for its two key materials: nickel (from the German Nickel, a shortening of Kupfernickel meaning 'devil's copper') used on the positive plate, and cadmium (from the Greek kadmeia, an old name for zinc ore) used on the negative plate. Knowing the chemistry is in the name helps separate it cleanly from the lead-acid battery it often replaces.
Why Pilots Care
It delivers high starting current reliably and tolerates deep discharges better than lead-acid batteries in many aircraft applications.
Intuition Check
Do not assume a nickel-cadmium battery behaves like a common car battery. It is a different type of rechargeable battery and may have different charging, inspection, and operating limits.
Example Sentence 1
The turbine aircraft's nickel-cadmium battery provided enough current to start the engine even on a cold morning.
Example Sentence 2
Maintenance replaced the Nickel-Cadmium Battery after it failed to hold charge during a cold-weather start.