Seiko 4M21

The Seiko caliber 4M21 is a kinetic quartz movement developed in Japan during the 1990s. It stores energy in a rechargeable capacitor (SL614) rather than a conventional battery, providing approximately 42 days of power reserve when fully charged. The technology originated as AGS (Automatic Generating System), introduced by Seiko in January 1988 before being marketed under the Kinetic name. The movement features a digital display and has been discontinued.