I gotta tell ya, it's a pain to remember to take off your watch to recharge it every day or so. And woe unto you if you forget! It's not user friendly at all. It's going to have to be easier than that, for people to keep using it.
Perhaps two sets of easily swapped watchbands, each containing battery, one charging while the other is in use.
Or an inductive charger built into a special electric blanket. The watch can charge while you sleep
Or some way to charge within seconds, perhaps with a large value capacitor.
Maybe constant regeneration via movement.
Something. Please!