Just a thought . .. are you backing up to iCloud? On a wifi to DSL (like I have) it would take hours. This would be in the background, but would show up as usage.
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no i'm not backing up anything to icloud. even though i'm signed in using my apple id to icloud, everything is turned off.
i charged my iphone 5 again to 100% last night, i just got home 14 hours later, now battery life is down to 85%.
my iphone 4 was charged to 100%, used approximately 40 minutes of usage time during those 14 hours, battery life was down to 91%.