best way to remove battery corrosion?

In a remote or toy with AA batteries? That white crust is from alkaline batteries, so a cotton bud dipped in white vinegar or lemon juice neutralises it. Gloves on, scrub gently, dry it, then rub the contacts with a pencil eraser or a bit of fine sandpaper if they're still dull. If it's a car battery it's the opposite, baking soda and water.