Because I have found that the battery of my new iPhone 4S went down more than 20% within 8 hours overnight while it was in the airplane mode with only the alarm clock app running in the background. During this period of time, the phone was never disturbed since I was in sleep and nobody else could touch my phone. Please take the poll with the percentage converted to the 8 hour period. For the data to be accurate, please report the percentage with the phone not used except for one or a few small apps running in the background (such as an alarm clock). Thank you for taking this poll!