I'm in the same boat...just got my 40mm Classic back from Samsung for diagnostics and battery replacement - didn't even make 8 hours yesterday. It sat fully charged on the nightstand and I woke this morning to find the battery down to 65%. Bluetooth and wifi were both on as a test (because why shouldn't they be???) Seriously disappointed!
Yea right. If I just want to use a watch I just buy a watch, not a smart watch. I'm wearing this only for 3 day and I don't like it already. The battery drain crazy fast.