How do you clean corroded battery connections?

Buy a tool especially designed for this, at most parts stores. Before you start to clean your battery get some Arm and Hammer or equivalent baking soda, put a small amount into a cup, fill the cup with water mix well and pour over the top and sides of the battery. This neutralizes the acid. Then use a garden hose to rinse off the baking soda. Let your battery dry then clean the terminals with the brush you purchased at the parts store.