Even with an unlocked bootloader, you would you never get to 4.3 because 4.3 was never released for this phone.
As for battery, when you updated to Kit Kat, did you do so with all your apps installed, etc and not do a Factory Data Reset?
I would really encourage users to do the following before taking the OTA:
- Backup whatever data you can to your PC or external SD card (pictures, etc). If you are rooted (and have an unlocked bootloader), then use a tool such as Titanium Backup to backup your apps and their settings. If you're not rooted and/or have a locked bootloader, then you won't be able to retain your app settings with TiBu. Sorry. That's the glory of having root I guess.
- Do a factory data reset BEFORE taking the upgrade. This will wipe out your user data completely, including application data.
- Apply the OTA and profit.
I have found my battery life is just as good, if not better, than under JB. People who are having issues with Wifi, Blue Tooth, battery life, usually have not done a FDR on their phones, so you have old cache sitting around, etc, that bogs down the phone as well as causes a host of issues.
The same holds true when upgrading Windows on your PC (for those that use Windows). I always backup user profiles and then I go and do a complete fresh install. There is so much gunk that gets left behind that it's just best to wipe the slate clean and start anew. The same goes for upgrading the OS on your mobile phones, especially when going from JB to KK.
KK is much better than JB, especially on this phone. No way I go back to JB. No way, no how.