i had the same problem,but now the battery-life of my NIT is perfect.what i can say is:
1. the USBcontrol can cause battery drain.
2. if you reboot (by terminal as root, not by the power button) it will surely solve the problem (if there is no hardware problem)
3. don't rely so much on cpu percentage usage!
and finally i suggest you to install the "advanced power" aplication( very useful )
i hope these can solve your problem
(sorry for bad english!)