Does you Apple Pencil 2 always charge when attached?

Hi! I noticed that my apple pencil 2 is losing charge after not using it awhile even when attached to the 2018 ipad pro. Re-attaching it no issues, always charges up to 100 percent then after that not using for sometime it will drop its charge, it even went 0 battery after a week or so. Is this normal? Does the apple pencil always charge when attach to the ipad or not? I mean do i really need to reattach it everytime so it will charge again.