Overfilling the battery, poor design of the vent cap, age and distortion of the gaskets can all cause battery terminal corrosion. Nitrogen gas is emitted by the electrolyte in the battery. Material in the battery terminals and cable ends reacts with the nitrogen gas, and corrosion begins to form.
Corrosion is a build-up of non-conductive material that breaks the connection between the battery and the battery cable. Battery corrosion can spread to other materials and has been known to erode the copper in battery cables. Inspection for corrosion should be done periodically. If corrosion is found, it can be removed by scrubbing the area with baking soda.