I have found interim relief for the battery drain issue after Android Pie update on Nokia 5 (hope this will also work on other phones like Nokia 5.1, 6.1, 7.1 and 8).
Things need to be done to check if it workouts for you:
1. Switch on battery Saver always(don't worry further setting told below will allow apps to run fine).
2. Turn off adaptive battery/brightness.
3. Tap 5 times on Build number in Setting(Settings> System > About Phone> build number) and turn on Developer mode.
4. come to Developer options (in Settings> System )search through all the option and let them all be set to off, the Background process limit and Don't keep activity are set to "Standard" and"off" respectively by default please don't change this....its Very important.
5. I also set the Window animation/Transition animation/Animator duration scale to "off" which drastically improved and eliminated few lags in notification bar/lock screen which I was randomly facing.
6. Lastly Give a REBOOT to device.
Doing all this my battery backup is same as on Oreo 8.1 on my Nokia 5, hope this will also work for you guys. Give a try