I left my charger at a friend's house yesterday and won't be able to get it back till tomorrow due to inclimate weather, so I thought I would just turn the iPhone off and turn it on twice a day just to check my texts. But when I shut the phone off this morning it was at 35% battery life, and when I turned it back on this evening it was at 16% battery life!! I guess I don't know much about lithium ion batteries but I just assumed it wouldn't drain at all in 12 hours if turned off. I haven't had major issues with the battery during actual usage (I get about 5 hours usage time, which I figured is pretty typical for a 20-month-old phone) but now I'm wondering if I should take it in to Apple for diagnostics while I still have two-and-a-half more months of AppleCare+ remaining. Has anyone else experienced this, and should I be concerned? Or is this totally normal? As an aside, I can't believe I have to wait another 24 hours to get my charger back... I hopped on iMore last night and bought a backup charger so hopefully I'll never have to go through this again! If only we hadn't had a terrible snowstorm today... Edit: Oops, I just realized maybe I should have posted this in the "iPhone Tips, Help and Troubleshooting" forum. My apologies! Mods, feel free to move this post if it is inappropriate for the general iPhone forum.