I'm having a similar experience. I did a factory reset, and still getting close to 4hrs of screen on time max. It sounds like there's 2 cells in the N7 running in parallen (3.7V, not 7.4V)... I wonder if one of them failed? Seems like the most logical explanation. It sucks to use it for browsing, etc and have it dying within 4-5 hours. Don't even get me started on games, even 2D games, which seem to absolutely slaughter the battery.
All this with brightness below 20% at all times. I used to get 7+ hours of screen on time no matter what I was doing... charging it every other day. Now I charge every day, and often times mid day. Going to try killing it tonight, let it fully charge overnight on the factory charger, then turn off the screen lock, set brightness to minimum, and just leave it on my desk. If it lasts 9hrs with wifi off just sitting at the home screen, then it stays. If it lasts less than 6 hours, then off to the ASUS monkeys...