My Motorola Droid RAZR MAXX suddenly started eating the battery much faster than it did just a couple of days ago.

I went to System Settings->Battery and discovered that the main consumer of power is now the Android OS, which has left Screen, the traditional battery hog, far behind.

I tapped on the “Android OS” line and found that the “Keep awake” time counter measures several hours per day, even when I almost don’t touch the phone.

After some browsing of the Android forums, I found that the culprit is this thoroughly hidden setting:

System Settings -> Wi-fi -> (menu) -> Advanced -> Keep Wi-fi on during sleep

Once I turned it off, the battery usage has returned to normal. I have never wondered into the Wi-fi -> Advanced menu and I was not even aware it existed. So, am not sure what exactly happened. The “keep on during sleep” feature could have been introduced by some recent update, or its default value could have been changed, or the meaning of the setting could have changed causing the Android OS to consume more battery power. Either way, turning this setting off seems to have solved the problem.