How to Clean Battery Corrosion
https://www.bobvila.com/articles/how-to-clean-battery-corrosion/

STEP 1: Protect yourself and your work surface.
First, set up a safe place to do the job. Spread newspaper over the surface where you plan to work, and since there are chemicals involved, it’s recommended that you wear protective gear.

STEP 2: Clean battery corrosion with a household acid, like vinegar.
Alkaline batteries leak, not acid, but a chemical that registers as a base on the pH scale. For that reason, it’s wise to clean a battery leak with a mild household acid like vinegar or lemon juice. Both liquids work to neutralize the alkaline discharge. Place a drop of vinegar or lemon juice onto the corroded area, then wait a minute or two for the neutralizing effect to take place.

STEP 3: Use a Q-tip to wipe up the corrosion.
Having dipped a Q-tip or toothbrush dipped into your chosen acidic liquid, gently wipe away the crystalline white residue from the battery itself and wherever the leak may have spread. Double-check the drawer where you store them and the compartment in the battery-powered device so that you don’t miss any of the residues. Again, be careful not to get the chemical on your skin or in your eyes.

STEP 4: Pick out the last of the crystalized leak with a toothpick.
Address lingering residue with a toothpick or, even better, a pencil eraser. If you’re cleaning the contacts within the battery compartment, sandpaper or a file may prove handy for the purpose.

Now, what do you do with the batteries that have corroded? Some municipalities allow you to throw in alkaline batteries with your regular trash. Other counties and states enforce more stringent regulations. Check with your local sanitation department for the appropriate disposal method.

3 Tips for Preventing Battery Corrosion
Going forward, there are a few simple things you can do to prevent alkaline battery leaks:

First, don't use expired batteries.
Second, don't mix old and new batteries; when replacing one battery in a bay, go ahead and replace them all. Even mixing battery brands commonly causes problems and should be avoided if at all possible.
Finally, know that batteries are highly sensitive to heat and must be stored at or below room temperature.