Baking Soda and water is the correct thing to use. The Corrosion is caused by acids and electrolisys. You need to nutralize the acids so you use baking soda... Carefully remove the battery cables, and gently scrub the battery posts with the soda paste. Do the same for the cable clips -- get the corrosion off and the surfaces clean. Be careful and wear eye protection, and a pair of rubber gloves. Watch out for stuff hitting your clothing as well -- it'll trash your outfit in a heartbeat. Rinse and allow to dry. Put a thin film of white lithium grease on the posts and re-attach the battery cables. Obviously, be very careful and make absolutely certain you've got them back on correctly. Wiring them backward would be very, very bad...