Clean out the battery recess with a toothbrush. Alkaline batteries contain a base, which is what corrosion is made of. An acid like white vinegar or lemon juice will neutralize this base. Lightly dip a cotton swab in white vinegar or lemon juice. Don't soak the cotton swab. Only use a small amount of liquid at a time.
Potassium Hydroxide The stuff (technical term) that leaks from alkaline batteries is potassium hydroxide, which is a very strong base with a pH of 12. It absorbs carbon dioxide from the air to form a feathery crystalline structure of potassium carbonate (11.5 pH).
For household batteries, this “acid” is actually alkaline – thanks to the potassium hydroxide chemical make-up. For lead batteries, sulfuric acid is the dangerous residue, which requires a different type of clean-up. How do I clean an alkaline battery leak?
The leaking batteries should be removed from the device and placed in a plastic bag for disposal in the trash. The best way to remove alkaline leakage from the device is to neutralize by carefully dabbing with a few drops of a mild acid like white vinegar or lemon juice.
Everyone has their own method of neutralizing alkaline damage, but the goal is the same: neutralize the alkali with a mild acid, flush the acid from the board and remove any moisture from the board. I use alcohol and compressed air while others may finish with water and heat.
The key is knowing what to look for and how to properly treat and repair the board. Moderate to severe alkaline damage is best left to the pro's. Soldering alkaline damaged boards is extremely difficult since in addition to eating away at the copper the alkali will get under the copper and destroy the adhesive bond.