Batteries, especially the rechargeable batteries found in most wireless keyboards, have a tendency to leak if they are left inside the battery compartment for too long. This is bad news, since the white crystalline substance that builds up on the terminal contacts is corrosive, and if left unchecked can do serious damage to the contacts and the wiring. Fortunately, the acid can be neutralized through exposure to CO2, such as that found in baking soda.
Remove the batteries from the keyboard while wearing chemical-resistant gloves. If they are stuck, gently pry them out with a butter knife or other flat, thin object. Lever the batteries straight up, and avoid applying pressure to either side of the battery compartment. Place the batteries in a plastic bag for proper disposal.
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Mix water and baking soda into a thick paste. Start with about a teaspoon of baking soda and add water a few drops at a time until it can be mixed into a paste with the consistency of cake frosting.
Apply the baking soda paste generously to any corroded areas using cotton swabs. Allow the paste to sit for 15 minutes.
Use a slightly moistened toothbrush to gently agitate the paste. Rinse the toothbrush often, and continue until the majority of the paste has been scrubbed away.
Examine the terminals for corrosion. Use a toothpick to scrape corrosion or paste from underneath the contact points if necessary.
Wipe away the remaining paste with a moist lint-free cloth. Insert new batteries only when the compartment has dried completely.