Battery started draining rapidly out in Xperia P after 3 months of use. I went to the service center and they updated the os and returned it to me. The problem persisted. So I followed the problem on the forum talk.sonymobile.com/message/304402 . Its almost proved that it is a hardware problem but the service center people are hesitating to replace. They say they will again test for a day or two and confirm if they will replace it or not.