Solar powered watches like Citizen Eco-drive, and similar offerings by Seiko and Casio, are brilliant timekeepers and avoid needing batteries replaced every few years.
They do have an eventual consequence of needing their capacitor replaced though most often this only is needed once a decade.
The capacitor can have a shortened life if they are allowed to deplete often, so for the best performance it’s best to keep them as charged as possible.
We know, depending where you live, sunlight isn’t always guaranteed.
When the watch is off the wrist:
Placing the watch on a windowsill with the face up will the best place to leave it.
Even if the sun visits infrequently it should be enough to maintain the charge in the capacitor.
When the watch is on the wrist:
Should stay charged without issue… as long as a winter jacket’s sleeve isn’t fastened around it the whole time.
Some solar powered watch manufacturers design their boxes to work as pedestals for catching the light better.
So be sure to make use of that if you can.