Spring Drive can be hard to “get” because it’s really a hybrid technology. There are quartz watches that have a mechanical component, of course – Swiss auto-quartz movements, as well as Seiko’s own Kinetic, use a rotor borrowed from an automatic winding system to generate electrical current; this charges a rechargeable battery in what’s otherwise a standard quartz movement. Spring Drive however is something different.
A Spring Drive movement has a completely standard mechanical gear train going all the way from the mainspring barrel right down to where you’d ordinarily expect to find an escapement and balance wheel. However instead of either, a Spring Drive watch has a “glide wheel” which contains a small, powerful permanent magnet. This rotates between two electromagnets, generating current to power a quartz timing package which in turn, controls (via the same electromagnets) how fast the glide wheel turns. This controls the speed at which the wheels in the going train turn under the impetus of the mainspring. There’s no battery or capacitor, and visually, the signature of a Spring Drive watch is a seconds hand that doesn’t jump; instead it glides smoothly (and silently) around the dial.