I realise this is going to buck the trend of most posters who are unhappy with battery life. Thought I'd share my experience to balance things up. I've had my Fenix 5 Plus titanium since February and logged battery life over several updates and betas. Initially I was worried I had a problem and avidly followed posts here about other peoples woes. At the 6.58 beta I experienced battery life matching Garmins claimed 12 days (HR and notifications on). At the 7.1 update I initially had terrible drain. A couple of hard resets have fixed this and I am now predicting 17 day with HR and notifications.
The setup I have is pretty well factory default except for the backlight set to 8 seconds and 20% brightness and I use the excellent Crystal watch face.
I say I am predicting 17 days based upon only using the part of my battery tracking where I have only used HR + notifications (I log battery % several times a day using Battery Widget by dsapptech). In reality I am now at 13 days on current charge having had 3 hours of indoor cycling (power and external HR sensors connected) and some minor GPS use. I currently have 4% battery left.
Clearly I'm delighted with my watch now, but I'm still amazed that we seem to have such a range of experience with regard to battery performance.