The iPhone 4S is the hot phone on the market, in more ways than one. There are widespread reports of disappointing battery life and of other hardware issues, such as excessively warm devices.
Scenario 1: iPhone 4S is working well. In my experience, with periodic phone use, and aggressive feature use--including Find My Friends, Find My Phone, multiple email accounts with "Fetch New Data" set to "Push" mode, all major notifications enabled, iCloud enabled, Siri enabled and used, and Reminders enabled to use location services--the 4S has more than enough battery to last a full day. With the screen turned off (say overnight), the battery loses just 2% per hour.
In the common configuration I just described, the GPS is essentially on continuously. A little-known tip about location services: to determine what application is using the GPS, run the Settings app and go to Location Services. Each application that has used location services has a grey arrow next to its on/off slider. Applications currently using the GPS have a purple arrow.
Another interesting tip: if you request a location-specific reminder, it turns on the GPS. To save battery life, turn off Location Services for reminders.
Of course many other features drain the battery faster than others. To save battery life you might consider cutting back in the following ways:
Minimize screen use. Turn down brightness (in Settings-> Brightness), and turn the screen off immediately after use (via a quick press of the power button).
Minimize use of CPU-using applications such as games, or even GPS software.
Minimize camera use.
Minimize voice and data service use.
"Push" email mode is known to use more power than periodic "Fetch" mode (Settings-> Mail, Contacts, Calendars-> Fetch New Data).
Turn off applications that use location services (Settings-> Location Services).
Turn off Wi-Fi.
Turn off apps that use notification services (Settings-> Notifications).
Use Airplane Mode (Settings -> Airplane Mode) if your phone is out of range of voice and data services or you don't want to use voice or data services. (Hunting for service is a larger battery draw than being in service range.)
To determine your current battery state, head to Settings-> General-> Usage and look at the "Battery Usage" section.
Finally, a general tip about "exercising" your battery: just as we humans need to get off our couches and move around, so do the electrons in the batteries of all modern phones. Performing a periodic deep cycle--that is, totally discharging and fully recharging the phone--helps to maintain or even increases the battery's electricity storage. Personally, for a new device I do a deep cycle twice, and then once per month thereafter. A tool like Battery Doctor Pro (http://itunes.apple.com/us/app/battery-doctor-pro-max-your/id340171033?mt=8) can provide useful information about your iPhone and its battery status.
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