Google's recently launched Pixel Watch ships with a small wireless charging puck in the box, as do many other smartwatches. Unlike some competitors however, the Pixel Watch isn't meant to be charged on anything other than its bundled charger. The information comes straight from Google itself. The company felt the need to clarify the situation by issuing the following statement sent to 9to5Google: Qi charging is not supported on the Google Pixel Watch. There may be some charging configurations where reverse wireless or Qi charging appears to work. This will be very device and charger...
Source: https://www.gsmarena.com/you_cant_charge_your_pixel_watch_with_your_phone_or_a_standard_qi_wireless_pad-news-56173.php