apple watch battery
Why does my apple watch battery show less than 10% when I go to put it on, despite it having been on the charger for 24+ hours? This happens about 30-40% of the time. I do not wear it every day.
Apple Watch
If your Apple Watch won't charge or it won't turn on - Apple Support
Reboot the watch, and check the charger and the cable and the contact. It’s also possible there’s a problem with the watch.
Once you’re through the above, best to chat directly with the folks from Apple Support.