Automatic watches are also known as self-winding movement. Like the name mentions, it is automatic so they don't need to be manually winded. The power of an automatic watch comes from the spring and the movement consists of gears. It is a smooth movement that has a rotor which is connected to the mainspring of the watch. Automatic watch movement pieces have great accuracy, but you might have to occasionally reset. Since the movement runs off of kinetic energy, there is no battery replacement, but again, you will need to have regular tune-ups.