Hi Igene,
I did a thorough check on the apps I downloaded, and realized some apps having background sync enabled (like every hour, every 6 hrs etc).
Will monitor the battery mileage over the next few days to see if there is any improvement.
Brightness level is always zero, wifi turned off, location turn off. it just drains very quickly.
Most of the time I had to use a second phone to do fb, twitter, take pic instead of the N4 for fear it will run out of juice when I am outside. =X
Anyhow, I believe some users may not face same problem as me.