The main body is a thin flat charger that holds one battery on each side. An optional base is included to plug the main body into, and sit on your desk to keep it organized and out of the way. When at your desk, the AC adapter plugs into the base; but when traveling, the AC adapter plugs into the main body. Charges any two Expansion Pack batteries at a time. An LED on each battery flashes to indicate that charging is in process and stays lit to indicate when charging is complete. Charging each battery takes less than two hours.