Everyone at one time or another has opened up the battery compartment of a device and found a white, crusty mess from leaking alkaline batteries. The acid left behind from alkaline batteries still needs to be handled with care, but it is not nearly as dangerous as some other types of acid, and anyone can clean up the mess and usually save the device.
Put on gloves and remove the old batteries. It is acceptable to dispose of alkaline batteries with your normal household trash.
Use cotton balls soaked with vinegar to clean and remove the acid. Be patient and take your time, throwing away the old cotton balls and starting with a new one frequently.
Soak a toothbrush with vinegar and scrub the battery contacts and other hard-to-reach areas after the majority of the acid has been cleaned up with cotton balls.
Dry the area with dry cotton balls and then use a piece of sandpaper on the battery contacts to rough them up and make a good surface for electrical conductivity.
Spray a small amount of silicon spray into the area and on the contacts to prevent any future rusting or decay, and you are finished.
Wear acid-resistant gloves and a long-sleeve shirt when handling any kind of acid spill to avoid any of it coming into contact with your skin.