Many watches today rely on more than simple winding to keep them running. Mechanical watches, such as those used since the dawn of timekeeping, rely on spring tension to keep the mechanism running. Once the tension is fully relieved, the watch stops. Quartz movements use a battery to keep their watches moving, but only until the battery dies. A third style of watch uses a capacitor, storing and releasing energy from a variety of sources.
What is a Capacitor?
Found in electronics of all types, capacitors are devices that store and release electrical current as needed. The capacitor assists the rechargeable battery in the movement in maintaining the proper amount of charge, potentially extending its useful life. Capacitors can store energy from a variety of sources of current, and in a watch, this amount of current is often very small. When the appropriate amount of charge is released, the resulting energy keeps the battery running. Watches that eschew batteries entirely in favor of capacitor-only designs eliminate the environmental impact of battery disposal.
Some watch manufacturers use solar energy as a power source to keep their capacitors charged. Although these solar cells require very little ultraviolet energy to maintain a reliable charge, some exposure to sunlight is required. These pieces often have small indicators letting wearers know the capacitor's charge state.
Hybrid-style movements that mimic the manner in which automatic watches stay wound with quartz, use the natural wrist motion of everyday wear to keep the internal capacitor charged. In turn, the capacitor maintains the proper amount of charge to the battery. Some of these designs do not use batteries at all, with the capacitor storing and releasing energy. These must be replaced at certain intervals.
Furthering the blend of mechanical and quartz movements are those watches which mimic the feel of a mechanical watch, while maintaining the accuracy and convenience of a pure quartz movement. These designs allow the internal capacitor to charge from winding of the crown, as a wearer would do with an automatic or manual watch. If the wearer forgets to do this, the capacitor and battery (if present) maintains its charge through normal everyday movement.