iPhone 13 mini iPhone charging issue

[Blarnld]

I charge my iPhone 13mini at night on a bedside lamp with Wireless Charging feature in its base. During the night I'm occasionaly hearing a soft chime sound. The phone is charged to 100% in the morning. Please see the attached screenshot of the battery levels during the night. Looks like something is not right. The phone is on iOS 16.3.1. I also have the app "Nightstand" on during the night. Any insight?
Thanks

 

[StumpyBloke]

Might be your sleep schedule? Mine makes the “time for bed” chime if I haven’t invoked the Sleep focus.

 

[Blarnld]

Might be your sleep schedule? Mine makes the “time for bed” chime if I haven’t invoked the Sleep focus.

I have not set up Sleep Focus, I just have a Do Not Disturb schedule set up. I'm not familiar with the "time for bed" chime.