Forgive me if this has been discussed but I have not seen any serious discussion about it. Many reviews of the Nexus 5 mention inconsistent battery life. In my humble opinion most of these are due to Google Now. I think the idea is fantastic and it is amazing at figuring out what you are doing and where you are going. I firmly believe in a few more development cycles it will become a major part of many people's lives. However if you analyze it with a good battery monitor you will find that it sometimes hammers the data connection and more importantly wakes up the phone almost continuously. Other times it is very parsimonious in its use of wakelocks or the data connection. I am certain Google is working on improving this but I absolutely believe that if one wishes to have guaranteed all day battery life the only way to ensure this is to disable Google Now.
I am curious if others have had or similar experience or wish to violently disagree with me. I actually wish someone like Anandtech would do an objective analysis of this. Some of my conclusions come from hard data from GSAM battery monitor but other observations are far more anecdotal.