That said, with all the fancy features this phone does come with (LTE, 2.3GHz Processor, 5" LCD) plus tons of software features, it can really suck down the battery life in a few hours. The first day I took my to work, from unplugging around 7AM to about 9AM (Yes, 2 hours), I noticed the power is down to 82% without even using the phone.
You can Google "Nexus 5 Battery Optimization" for a whole lot of tricks, but I don't want to do things like "turning off 4G" or "disable GPS" which impacts the fundamentals of the phone. I have discovered the following formula which seems to be the best power to battery ratio.
1. Manually adjust your Brightness Settings; the default Auto Brightness is much more aggressive than previous NEXUS phones, perhaps future release will fix this; I set it to roughly 20% of the slider and find it plenty bright.
2. Set Auto Dim to 30s from default 2 Minutes
3. Disabled the "Ok Google" Hot Word detection (Press Empty Space on Menu>Settings>Voice>Hotword Detection off
4. Turn off NFC and Bluetooth (when not in use, I rarely use these features)
5. Watch out for Widgets or Apps that sucks power: I was using a widget for clock and weather, and for whatever reason, on the Nexus 5, it was using so much power, more so than LCD Screen in the battery analysis, so I uninstalled it.
6. Push Notifications: I only have it on for default or utility stuff (ie. Hangout/SMS, Google Voice, App Updates and Emails); I turned everything else off such as news and alerts.
With the settings above, I monitored my battery throughout the day; by from 7AM to 11PM, the phone has light to moderate usage throughout my work day and still end up with 62% of power left... Not bad at all.
UPDATE: I purposely not charge the phone when I went to bed, I woke up in the morning with 52% Power left. After 24 hours, 54% remaining. Thats pretty darn good.