There are several app settings in your wearable that will influence battery drain, connections (BT, WiFi, NFC, etc), display (Always On !! don't use it, brightness), monitors (HR, etc). You'll need to go into the settings and walk around the areas and google out the settings to figure out your unique combinations of need.
Yes BT will put a drain on your device but not as much as other settings do.
The device while capable of doing a lot of things isn't designed to do all of those things all of the time and our social culture often demands things technology has yet to catch up on. So yes they've been around a while but these things aren't replace-ables for smartphones (yet).
I have down loaded 6 additional professional watch faces to wear my device primarily as a watch, with added features. I have a 3g phone version (connected to a Galaxy Note 4), and I get 20+ text messages a day, 3-10 phone calls and emails (notifications of these things too). I have a map application and the s-health app (which I am hoping to replace my Fitbit charge with) when sleep tracking finally catches up. My device currently lasts 40 hrs before it goes back in to the charger with 15-20% charge remaining.
BTW, the first 2 days I had the wearable (S2 classic) it didn't last more than 4-5 hrs but it had everything turned on and connecting as often as it could.