I see you are a new user - welcome to Android Central! Before doing a factory reset, perhaps try the following options:
- put your S8+ into Safe Mode and see if the battery life/lagging still persist. If not, then it is likely an app that is causing some issues for you
- check out your battery usage stats. Perhaps there are a few apps running in the background (maybe they're not updated to the latest software, as well) that are causing a bit of a hog on your battery
--> screenshot your battery usage stats to us so we can assist you too!
--> if you use a battery-intensive app like Facebook or Facebook Messenger, there are some browser Facebook apps that do most of the same functions as the regular app and will use less battery
- have you downloaded any new apps or started using a new launcher or any kind of widget in the last week or so? Sometimes those things can affect battery life as well