I agree with RW, but use a q-tip, considering it's a small appliance. Hold the appliance downward, so as not to cause moisture damage to internals. If still green or gray, rip off a strip from an emery board, wrap unto a toothpick, sand off the corrosion.
Baking soda and water will neutralize the acid produced by the battery. Then simply clean it with sand paper. You can also go to the local wall mart-mart and get a CRC chemical battery cleaner.