As a sort of early holiday present, Samsung announced that the Galaxy S9 and S9+ would be updated to Android 9.0 (Pie) from December 24 onwards. However, few regions have actually seen the upgrade for these devices as yet. Some users who have managed to install it may face more battery drain than usual.
https://www.notebookcheck.net/Galaxy-S9-series-reportedly-experiences-battery-drain-on-Pie.388066.0.html