You just got the beta, it takes at least 2 days to learn usage patterns if not more. Give it a week, if it still doesn't get better then there is some issue. My battery now is the same as it was on pie.
Samsung is working on the next update. It will be released soon for the S9/S9+ with fixing all the stuff. Already the same issues has been fixed in the Note9 which got the 2nd beta update today morning. So soon will be there for S9 too.
