I got a 5s about a month ago, AT&T. It's still with its original 7.1.1. Battery life has been great until the other day when I noticed in the evening with almost no use throughout the typical day it had dropped to below 10% and draining fast. Nothing different in reception or apps (I only keep Safari and Mail open). The only thing that I can think of as different is that recently the iOS 8.1 update prompt popped in my settings. It was downloaded automatically but I haven't installed it yet and there's an option to delete the update. Any thoughts appreciated.