It appears that iOS 5s GM release introduced a bug that causes the Setting Time Zone function to keep the location tracking circuitry running constantly, draining battery power considerably. Switching it off may mean that your iPhone will no longer set its own time zone when you travel, but that's a small price to pay for having your iPhone last more than 12 hours on a full charge...We have tested this method on 4 different iPhone 4S handsets, including an iPhone 4 and an iPhone 3GS. All have reported drastically improved battery life after switching "Setting Time Zone" off.