If alkaline batteries formed the corrosion, baking soda (which will neutralize acid) won't do squat.Try 5% vinegar solution, applied sparingly with a cotton swab. Then, as a precaution, use the Baking Soda solution to neutralize any residual acicity. Dry well. be VERY careful using an abrasive like sandpaper wch will remove the plating on the contacts if used too vigorously.An old-style typewriter eraser- which contains a mild abrasive- if you can find one, is a better choice.

Good luck!