Definition
A liquid or paste inside a battery that conducts electricity by allowing charged particles (ions) to move between the battery's positive and negative plates. In aircraft lead-acid batteries, the electrolyte is a mixture of sulfuric acid and water. In nickel-cadmium (ni-cad) batteries, it is a potassium hydroxide solution.
Plain English
The chemical liquid inside a battery that lets it produce and store electricity. Without it, the battery cannot work.
Context Anchor
Seen in aircraft battery descriptions, servicing instructions, and maintenance discussions.
Derivation
From the Greek 'elektron' (amber, the original source of static electricity) and 'lytos' (able to be loosened or dissolved). Literally 'something that loosens under electricity' -- a fluid in which electric current causes the chemical components to separate and move. That is exactly what happens inside a battery.
Why Pilots Care
Battery performance and aircraft electrical reliability depend on correct electrolyte level and strength; low or contaminated fluid can cause starting failures or electrical system problems.
Analogy
Similar to the liquid inside a car battery that allows it to deliver power to start the engine.
Intuition Check
Do not assume electrolyte always means ordinary battery acid. In many aircraft batteries it is an acid-and-water mixture, but in other batteries it may be a different chemical; its job is still to carry electrical flow inside the battery.
Example Sentence 1
During the 100-hour inspection, the mechanic checked the electrolyte level in each cell of the lead-acid battery and topped them off with distilled water.
Example Sentence 2
The mechanic replaced the electrolyte after discovering it had become contaminated with debris.