My phone lasts more than a day of typical use on a charge ("Standby time: Up to 10 days"). When I'm using my laptop for anything more than an hour, it's easy (and not inconvenient) to find an outlet and plug in.

For a watch, 18 hours might not even cover a full work day.

That's my point though - I have enough devices to charge already. I'm also very used to charging my phone and laptop - I change my watch battery once every couple of years or so.