A watch that needs to be put on a charger? Smart is not exactly the word I would use for such revolutionary design.
Presumably this is a product for the same market that wants to plug in their glasses :P
With something like pebble, I wonder how much energy is necessary? Could some well-placed solar cell on the watch do the trick (think calculators).
If I could get one wish in life, it would be to have something like nuclear batteries we always see in sci-fi (actually, there are probably 12 other things that would be more important in the long run)
But that's still not enough power to drive the screen on most "smartwatches". Nor their higher power cellular/wifi components.
Fact of the matter is, TFT screens eat batteries like no-one's business. No avoiding it. E-ink screens would do better, but have nighttime visibility problems that would be hard to overcome.
Plain and simple, the undoing of the smart watch is the battery. It's an obstacle we may someday overcome, but until that day, it's not likely to catch on and become the big hit everyone wants it to be.
My Casio watch has two tiny solar panels built into its face. According to the manual, 5 minutes of sunlight each day (or a few hours of indoor lighting) is enough to compensate for normal use, and the battery will last 6 months even without any sunlight.
I've had the Casio for 9 years now. It still works fine, and I've never had to manually charge or replace the battery. The battery does get a bit low in the winter when the watch spends a lot of time covered by thick clothing, but that problem is easily fixed by leaving the watch in the sunlight for a few hours when spring comes.
Sure, it's not "smart", but it can display the time in several different timezones, act as a stopwatch, and even has a button that lights up the display at night (which will probably drain the battery faster). All running off of two solar panels the size of the nail on your pinky.
That sounds overly pessimistic. Computing power per watt has improved by several orders of magnitude over the last couple of decades already. Combined with more energy-efficient displays (anyone wants to improve on e-ink?), who knows what we could pull off 5-10 years from now, even without a significant change in battery capacities?
300K * k * 1GHz = ~4pW
Or, in other words, you are right, we can in theory reduce the power consumption of our computers so much that a current watch will last for a lifetime.
Even disregarding that for e-ink, there's the radio, which is limited by the channel capacity, from which I'd say we're also less than a magnitude away for isotropic radiation.
The actual technology for this has been around for long time. I'm aware of at least two startups that tried to commercialise it but they faced the chicken and egg problem of (1) getting manufacturers to make changes to their devices/batteries and (2) getting enough the charging pads in enough places to for it to be worth the everyone's time.
Neither company survived but I suspect this was a market-timing problem. Given the wide proliferation of devices (phones, tablets, etc) some solution will eventually get adopted. If those companies were starting now I think they'd have a better shot.