iPhone 4S battery life has been known to vary greatly among users without solid answers as to why this occurs. Some people have proposed iOS bugs and others have found fixes via toggling Time Zone Support, Exchange, Siri, Notification Center, Stocks/Weather Widget, and a few other features. Some have found increased battery life performance after hard resets, full phone restores, or even simply letting the battery complete a few full discharge/recharge cycles. Unfortunately there is no 100% accurate method to determine what feature of iOS 5 on an iPhone 4S is using your battery to what extent, nor is there any sure way of knowing if any of the above steps would have an effect (positive or negative) on the battery life of the end user's iPhone 4S. Developers may have certain additional tools at their disposal, but the majority of people world-wide do not. What we do know is that the Settings app contains a rudimentary Usage statistic (Settings -> General -> Usage- Battery Usage) that can tell us how much time has elapsed since the last full charge cycle. Under this Usage statistic, Standby time is defined as the number of hours that have elapsed since your phone received power during it's last full charge cycle, or in simpler terms- the total number of hours since you unplugged your phone. It is not specific to "pure" Standby time, meaning that this number counts the time while the phone is idle with the screen off as well as the time that you spent using your phone. If I charge my phone to 100% and then unplug and use it for 1 hour straight, the Usage time will be 1 hour and so will the Standby time. Standby time therefore = total time inclusive of usage. It is impossible to accrue Usage time without also incurring Standby time. As previously mentioned this is a rudimentary statistic and therefore "Usage" is extremely difficult to define and is essentially "any and all phone usage." Therefore while some may be able to check this counter and find 10 hours of usage, others may only see 4 or 5, depending on what they were actually doing on the phone. There is no distinction made between 1 hour of iphone use at xWatthours or 1 hour of iphone use at 2xWatthours. (Averaging battery life from multiple users over a large length of time would not be a very accurate indicator of true iPhone 4S battery life and does not make up for this discrepancy in usage detail.) I decided to conduct a simple low-tech experiment over the period of 1 week in which my usage was very similar day to day and recorded by me in detail via notepad.txt files on my pc. I decided to "screenshot" the usage statistic everyday once the phone hit 20%, +/- 2% and observe how battery life varied depending on which features were enabled or disabled. A hard reset was performed after enabling/disabling any feature. One (sometimes two) feature(s) was disabled each day and re-enabled the next day in exchange for another. Screenshots: Uploaded with ImageShack.us Wifi is on for 100% of the time during this entire 7-day test. 3G was enabled between 5-15 minutes per day however no more than 2MB were downloaded via 3G on any given day. The camera app was used to take 5 Non-HDR pictures with the rear camera, and 5 pictures with the front camera. Thirty minutes of Facetime are included in each day. Two 30 second videos are recorded each day. Notification center was accessed a total of 12 times per day. Google maps was not used at all throughout this test. Siri was used 2 -4 times a day for weather (location based) and reminders (not location based). I have 3 email accounts, two are fetch gmail and one is a push exchange. Between 8-10 emails were sent from the phone daily and between 20-30 emails were received. e-mail size was no more than 1MB max. iCloud is on. Photostream is off. iMessages and texting were used for 50 - 75 messages a day. 60 minutes of talk time were included each day. Other apps that I used with consistent usage everyday: WhatsApp, Opera, and Google Voice Day 1 This day's test-feature usage: 100% brightness + auto brightness Off (all other usage identical to all other days included.) Day 2 Brightness reduced to 60% + auto brightness turned On Expected battery life to be more, it was not. Day 3 Notification center is disabled. Brightness remained at 60%. Day 4 Notification center is re-enabled. Stock and Weather widget are disabled. Brightness 0%. Day 4 Later: I was asleep from midnight to 4am. The phone should not have accrued 4 hours of usage but it has somehow. I received only 3 emails between the time these two screenshots were taken. No missed calls or other app notifications or alerts other than the 10% battery life remaining pop-up. Day 5: Stock and Weather widgets are re-enabled. Brightness is back to 60% + auto. Day 6: Turned Siri off. All other above mentioned features have already been turned on, brightness still at 60%. Battery life is increased dramatically and no more mysterious usage occurs when I'm not using the phone. Day 7: not sure what else to do. Turning Siri back on will probably result in worse battery for me. Not sure if this is helpful or not but I had all this information so I figured it might be worth posting. Feel free to comment, critique or ask questions. This is my first attempt at recording my usage so thoroughly so hopefully suggestions from the community can help improve the methodology for the future. Individual results may vary. For me, it seems Siri and brightness have the biggest impact on my battery life. Does Siri really cause mysterious background use? More testing is probably needed to fully reach that conclusion.