The toothbrush chargers works with an oscillating magnetic field

I am not sure what the Seiko looks like inside, but it must have a mass that wiggles with arm motion and moves a magnet through a coil of wire like a small version of those flashlights you can shake. By placing the watch on the charger, the oscillating magnetic field in the charger will induce a current in the coil and wiggle the mass at 60 Hz.

I would worry that the induced current may be higher than what would normally be seen, and could burn-up/overstress components, or even the wire of the coil. This could be regulated by placing the watch at a farther distance from the charger at the point where it charges at a "natural" rate.

I worry a little about magnetizing effects, but since the field is oscillating, it really acts more like a de-magnetizer. I am concerned that the magnet in the watch may become demagnetized so that the watch won't charge at all when you shake it.

Also, the coil and mass are being subjected to a 60 Hz movement which could cause damage since they are not designed to move so fast.

Interesting stuff.

Scott