I think the "5 day claim" was for the 46mm non-LTE version of the watch. The smaller versions and LTE version of the watch should see less than that. Also, I'm sure the 5-day is with little use, screen set to a low setting and the always on display set too off.
I have the 46mm LTE version and keeping the sceen on all the time (AOD on), I'm getting about 2.5 days between charges. My guess is I'll get three when the newness of it wears off (and I stop playing with it).
For me the battery life is far better than what I had on my S3 (and I had both LTE and non-LTE version of the watch).