While the battery is a significant update on the Pixel 5, it seems there's an issue on the software side. Users have been reporting that the battery indicator gets stuck at showing a certain percentage even after some time has passed. 9to5Google reports that a unit of one of their writers took over three hours to go from 100% to 99%.
Google acknowledges that this is a known bug and it promises to roll out an update to fix this problem. One temporary remedy is to restart the phone and plug it into a charger to correct the percentage it shows.