Why do battery terminals fur up?

Battery terminals fur up due to a combination of corrosion and oxidation processes. When the battery is in use, hydrogen gas can escape from the electrolyte, reacting with lead or other metals, leading to the formation of lead sulfate or other compounds. Additionally, moisture and contaminants can exacerbate this reaction, resulting in a buildup of white or greenish deposits. This corrosion can hinder electrical connections and reduce battery performance.