Why doesn't my Garmin Fenix 2 battery last all day?

It sounds like your are having issues with your battery. You should go through some troubleshooting steps to try and diagnose your problem. Please refer to the battery replacement guide for the Garmin Fenix 2.

I faced similar problems after the recent update. A "hard reset" didn't help either. I performed a "roll back" to software ver. 4.40. After a full power cycle, everything is back to normal for me ( 8 % battery life per day).