A couple of things come to mind. This is caused by the electrolyte migrating to the terminals. There are buffers that can be placed between the terminal and the battery box to reduce electrolyte migration. They do work. If the top of your battery is always moist, you know that you may have a problem. Sometimes, it’s from people servicing your battery and overfilling the cells. The electrolyte bubbles out and makes a mess. Clean the top with baking soda and water and a soft brush. Be careful not to get that on your clothes or in your eyes. Cleaning the top will improve the situation dramatically.