I stumbled upon this thread on the official english MIUI forum: http://en.miui.com/thread-279237-1-1.html The author suggests turning off automatic contrast and automatic date/time, as it might have a positive effect on battery consumption, and it looks like the theory might be correct. I turned off the automatic contrast a few days ago (I had never seen that option!), and battery does seem to last a little longer now, but I have other apps installed to minimize consumption, so I can't be sure what caused the effective result. If anyone having battery issues could try this, I'd appreciate the feedback. Because, if the problem is as simple as this, MIUI will surely fix it with ease!