Update 9/13/14: The battery is better but still nowhere near the 7 hours screen on time and 40+ standby of old times.
The battery life was really bad after the most recent two updates, even though they claimed to fix the battery drain bug in them. My last resort was to install the newest CM Nightly (9/07/2014) on it, and the difference is HUGE. I am finally back to the way things were when I first purchased the phone. The battery lasts
2 days over one day and gets over almost 5 hours of screen time again.
That’s it, if you want to go back to the way things were, install the newest CM 11 Nightly and enjoy the difference. It will not void your warranty, but do it at your own risk. Also, don’t forget to install the camera apk from CM 11s to enjoy 4k recording and switch to ART for better battery. Many of the software bugs are gone now, the only bug that remains is the touchscreen ghosting/jumps, that will supposedly be fixed with a future firmware upgrade.
Guide to Unlock Bootloader and Flash Recovery: https://forums.oneplus.net/threads/guide-oneplus-one-how-to-unlock-bootloader-install-custom-recovery-and-root.64487/
CM 11 Nightly: http://download.cyanogenmod.org/?device=bacon
CM 11 Gapps: http://wiki.cyanogenmod.org/w/Google_Apps
CM 11s Camera APK with 4k: http://forum.xda-developers.com/google-nexus-5/themes-apps/app-cameranext-one-plus-one-cm11s-t2730715