One of the surprising issues coming out of iOS 5 and the iPhone 4S is batteries which drain very quickly. Some users are even reporting drains of 10% per 15 minutes in certain conditions. For some cases, this has come down to identifiable issues like corrupt contacts. But a general trend of short battery life has come out.
Now, engineers have found a common thread - Location Services. It appears that in some circumstances, the "Setting Time Zone" function comes on when it is not needed, and can come on constantly. GPS drains significant power, when it is constantly on.
TIP: WORK AROUND THE BATTERY-DRAIN BUG IN IOS 5This is not the ONLY reason that iOS 5 can have worse battery life than iOS 4. Be sure to check and confirm you are not overusing Notifications, Find My Friends, or other power-hungry features if you try this fix and are still getting poor battery life.
To turn off the "Setting Time Zone" function to maximize battery life:
1. Open the SETTINGS app
2. Tap the "Location Services" option
3. Scroll all the way to the bottom and tap the "System Services" function
4. "Setting Time Zone" is 5th from the top. Slide it to OFF
Keep in mind that this means if you DO travel, you will need to set your time zone manually. But that may be a small price to pay for an extra 2 to 4 hours of battery life between charges.