The white substance which you see around battery terminals is either lead sulphate or anhydrous copper sulphate . Anhydrous copper sulphate changes to blue colour when water is added to it. The bluish substance which you see around corroded copper terminals or copper clamps is hydrated copper sulphate.
Cleaning Corroded Battery Terminals:
To clean lead sulphate or copper sulphate from terminals, first disconnect terminals from battery. Make sure, you are wearing gloves as these chemicals can affect the skin. Now, wash terminals with clean water. If rust washes away, then no more hassles. Otherwise, wash them with the solution of any of these bases caustic soda, washing soda or baking soda made by dissolving base into water. Simply dipping battery terminals or clamps for few minutes into solutions of these bases also works. After cleaning with base solution, wash terminals again with clean water to clear away the remnants of base.
It is advised not to pour the solution of any of these bases over battery posts to clean them as it might gain access to battery interiors through vents, joints or leaks. If entered, it can badly affect the performance of battery. Instead, use a cloth dipped in base solution to clean them or use a brush to rub the rust off. Take extra precautions while cleaning hydrated copper sulphate which is bluish in colour because it is poisonous.
Prepared solutions are also available in markets to clean the corrosion. You can also use them.
Prevention from Corrosion:
1- Corrosion can occur in dry environment but it is boosted by moisture and salts present in water. Therefore, keep the batteries away from moisture and damp places.
2- Do not wash interior of car engine bay with water. Water increases speed of rusting metallic parts of engine bay which are not covered with paint and also joints of power cables and battery terminals.
3- Always keep the battery top dry and free from dust and other pollutants. After pouring water into flooded lead acid battery, never forget to dry the surface of battery. Close the caps of individual cells tightly.
4- Apply Petroleum jelly or grease to battery terminals to protect them from corrosion.
5- Use clamps and battery terminals made from good quality copper which are also alloy plated. Layer of alloy prevents terminals from corroding.