I noticed this a few weeks ago but couldn't figure it out. It all made sense to me today though.
I always have my 9630 set to 1XEV for it's network setting. I checked it a few weeks ago and it was in Global. No clue how this could have happened. Well, last night I updated my google maps and did a reboot as usual. Today I just happened to check my mobile network from the options, and to my surprise it reverted back to Global.
So be sure and check your settings after a reboot. Could possibly be effecting signal strength and battery usage as it searches for cell towers?