Ha! This happened to me too! I went to bed, and as usual, put my phone in Offline mode, battery was about 70%. In the morning, phone was off, I thought that was weird, I didn't switch it off last night. Then tried to reboot and it only got as far as the Nokia hands then died again. I thought the battery was f*cked, but charged it in an external charger, and everything is fine again. Battery Eye graph shows that during the night, the battery drained down from 70% to zero in about 2 hours, from 11pm to 1am. Stranger than strange.