There looks to be a new update out on Windows Phone 8.1 for those in the Preview for Developers program. Yesterday's update to Battery Saver hinted at a new build (14203) for Windows Phone coming soon. It would appear that particular build is now rolling out. Time to check your phone for updates.
This new build is notable for enabling a 'real-time Live tile' for the Battery Saver app on Windows Phone 8.1. It also allows you to add Battery Saver to the Quick Settings found in the Action and Notification Center.
To check your phone right now for an update go to settings -> phone update -> check for updates. If you're enrolled in the Preview for Developers program, you should see an update. Look for the 8.10.14203.306 update to be available after checking.
We're still installing right now, but do let us know if you find anything else different in this build for Windows Phone.
Update: Below is what the improvements to Battery Saver look like. You get a real-time Live tile if you pin the app to your Start screen and you can now add it to your Quick Settings.
Thanks for the heads up Mark T!