Why is my Apple Watch Series 9 not charging fully?

My Apple Watch Series 9 started to not charge to full capacity on it's own . All i did is touch the watch on the battery power icon and it gave me the option to charge to full capacity again . Took me about 2 seconds to fix the issue , When i checked to see what my watch was doing on the charger , it stated it was charging to full capacity !! I hope this helps you guys, i know i was pretty mad when my watch wouldn't charge all the way, i haven't even owned it a full year yet and thought it was malfunctioning already.

[Re-Titled by Moderator]