This is an automatic watch which is powered by the wearers movement or by winding the crown. There is a rotor that oscillates within the watch so that as the wearer moves their wrist, the rotor spins to charge the watch and stores the power into the mainspring. If not worn regularly or not being moved enough, you can manually wind the watch using the crown to power the internal mechanisms. This type of movement is typically found in luxury watches and makes it run without the need for any batteries.