I must say that I've never had a phone that has had 7 hours of screen time before. Sure, the battery lasted "only" 12h 22m, but that screen-on time is IMPRESSIVE.
Yeah, the screen is pretty battery-efficient in this phone. It's the other background drains that 4.4.2 needs to address and we'll have a real winner here. We've proven the 24 hour usage time is possible with 'normal' use, but no way this phone even comes close to the 'up to' 10 day stand-by time advertised without some modifications to Kit Kat.