It isthe same thing as with the S7. Huge battery drain after multiple updates.
Wiping cache drive does'nt work anymore. I feel that the battery drain on the S8 is on purpose, so you will be tempted to buy a new phone (or battery). Samsung did the same when the S8 was launched and all S7 got an update with a huge battery drain as a result. They fixed that after a few weeks with an update after huge complaints, but this time it has not been fixed. I contacted a member of the European Commitee that i know and i asked them to investigate this. If they find anything this will result in a huge fine for Samsung. i still had galaxy phones from the first model. After 10 years the battery would still hold its charge well after 5 months being shut down (85%), and if used moderatly and in standby it would have a batterylife of more than 10 days. And this is when it was already 10 years old! So dont tell me that Lithium battery technology has gotten worst in 10 years time. I i would recommend Samsung to fix their problems and find another way to persuade people to buy a new phone.