I have an update. I finally went ahead and replaced the LCD panel as a last resort. To my great joy that fixed the problem. Someone on another forum pointed out that it most likely is caused by a broken DC/AC converter in the screen. If it is not the screen, it could also be the cable connecting mainboard and screen. If ASUS claimed that they replaced the screen under warranty they might be lying.
I have the same problem with the screen flicker. Changing the battery with a new one changed nothing. Just letting you guys know. My last resort would be changing the whole screen. But not sure becasue everything works fine when plugged into the wall.