Corrosion is usually caused by humidity, acid buildup, or decay. When it comes to batteries, corrosion is usually taken care of with a solution of baking soda and water. However, you do not want to put water into your Xbox. The safest way to clean it off is to avoid liquid period. Use baking soda and a toothbrush to remove what corrosion you can and then cover all metal surfaces with dielectric grease. It is not electrically conductive and will protect anything metal from moisture and acid. Just don't go crazy and cover the entire PCB in grease. A little bit goes a long way. Just a very thin coat should do. Dielectric grease can be purchased at any automotive shop or online for fairly cheap.