In my experience with the three Nexus 5's in my family, KitKat manages battery life quite well.
That said, I'm now running the relatively new Qualcomm BatteryGuru App. It's designed specifically to manage devices with the Snapdragon chip. It will not work on any other chip. It doesn't do any management for the first 4 to 7 days after initial install, as it's busy collecting usage data & patterns unique to your phone usage. All the while it counts down in days and hours till it will begin serving you. This is displayed in the notification area.
Once mine began managing my battery the results were outstanding. I now enjoy a minimum of 30% battery life when using lots of resources. For simple daily tasks I get as much as a 55% increase in run times. I endorse this app for those looking to let it manage their phone for best battery life. It turns wifi on and off automatically as needed and more. I don't have to disable or manage anything.
🙂
https://play.google.com/store/apps/details?id=com.xiam.snapdragon.app&hl=en