Nah, too bulky and there are already better solutions. If you have just a classic watch, then a kinetic charging mechanism is something that's been around for ~100 years. Your watch auto-charges from simply wearing it and walking around.

But if you need more juice, then solar watches are also a thing that work pretty well.

For a smartwatch, these batteries won't produce enough power to keep them going. It's better to just slap a bigger battery into the watch rather than a nuclear battery + regular battery.