Why has my GSIII's battery life dropped from 50-60 hours to 16 hours? I have a GSIII (Sprint) running Android 4.0.4.  In the last three days, I have not made any changes or installed any new software that I know of, but my battery life has dropped such that my phone, when fully charged in the morning, now powers off sometime before I go to bed.  This would make sense if I spent a lot of time using it, but I generally will check a few emails (every 20 min or so) and make maybe 4 calls of 5-10 min each in a typical day.  I have not varied this pattern lately.  I used to have to charge my phone maybe every other day, sometimes when really slow I could squeak 3 days out of it before charging.

Battery usage screen shows 'Cell Standby' taking up 40% of power usage.  I hadn't been looking at battery usage lately, but it strikes me that when I first got the phone (3 months ago) I checked these a few times and Cell Standby was fairly low, around 10% as I recall.  

I usually keep the phone on WiFi because of Sprint's crummy network, and the phone was in my house the entire time it was on battery, so was on WiFi for data...and WiFi takes up 3% of the total.  Display takes up 2%.  

I remember on my previous phone, the Evo (original) there was a Dialer bug that caused a wake-lock of some sort...I'm presuming something similar here.  Several hard power cycles have not improved matters.

What do I do to stop it, or find out where the CPU cycles are going?

Edit:  taking a look at the battery pane of the settings app reveals that the phone is staying awake 100 percent of the time that the radio is on.  It did not used to do that. Putting the phone in airplane mode lets the phone sleep as usual except for a few times in three hours, as expected.  So, apparently this is a wake lock condition again.
Cell standby being high means you have a really weak signal wherever your phone was.  The phone cranks its radio up to maximum power to try to maintain a usable signal.

There are several ways to stop it - none of them ideal:


Put the phone somewhere with a better signal (near a window maybe)
Put it in airplane mode to turn off the radio (but you won't be able to get phone calls/texts)
Switch to a carrier that has a better signal near your home/workplace


As for why it's doing it now, it could be that you're leaving the phone in a different place in your house most of the time, or weather is affecting the signal strength, or sprint is extra crummy in your area lately.