Indeed it’s not normal.
I would try to let the battery die, charge it completely and see.
I would also cut every source of battery drain. You could see which apps are using the run in background and boot up permissions thanks to this method.
If you are connected to a /e/ account, try to disable some synchronisation to limit data transfer.
Cut bluetooth, wifi, LTE, NFC, vibration on touch or whatever you don’t use.
If nothing works, before going back to the stock ROM, reset your device. Maybe some magic will occur 
Or it’s just a battery issue and you have to change it.