As per this post, I will explain more in detail and video at the very below of the post whereby you could get a notification when your Samsung phone or tablet battery fully charged. You are not required to install extra app for this as it come with Samsung One UI. (Starting from S10 I think) For other phone, maybe you could install the APK from trusted source. (Or just buy Samsung phone 😂🤣)
Samsung also implement this option in Device Care as per below.
Kindly refer to the below for the video.
Click here for iPhone or iPad