gonna just ignore the required information since its just item description related and not actually game mechanics related.
in short, beast gems, atleast bat gem lacks its experience bar, and it doesnt seem to buff properly nor level even after killing monsters, or show what it actually does.
this is how it should look like roughly from korea side:
and this is how it looks in here:
so as you can see, its missing “what it does” and “exp bar” from it, even after adding it to weapon it wont show what it actually does.