updated 06:59 pm EST, Thu December 20, 2012
Could come from increased number of Wi-Fi checks
MacNN and other tech outlets are seeing some user reports that the latest release of iOS, 6.0.2, is causing additional battery drain on at least some devices. Reports of issues first surfaced on Apple's own support forums, and so far seems to be limited to only some of those who were able to upgrade to v6.0.2. Apple's recent iOS and OS X updates have both suffered from scattered reports of battery drain compared to previous versions of the respective OS, though the company generally fixes them over time.
Adam C. Engst and Michael Cohen of TidBITS theorize that the problem may have its root in the increased number of Wi-Fi checks performed by the update to try and solve Wi-Fi connection issues, after performing some basic tests. Engst has recently updated his report that turning Wi-Fi on and off and unchecking "Ask to join networks" may also alleviate the problem for some of those who suffer from it. Overall, however, users generally report that 6.0.2 does indeed fix Wi-Fi connection issues that had been a problem in the earlier releases of iOS 6
On TidBITS' own comments, numerous readers report that they aren't having the issue, while others say they are experiencing it, making the issue hard to pin down. The 6.0.2 update is limited to only the iPhone 5 and the iPad mini, and thus those with older iPhones, or iPod Touches or iPads (even the current models) won't see this specific draining problem. Common causes of unusual battery drain can include background apps that are continuing to function (such as Internet radio), Bluetooth on when not in use, screen brightness not set to automatic and excessive push notifications, which turn the screen on every time a new one comes in.
The reports come on the heels of ongoing lower battery performance in Mountain Lion which are still not fully resolved but are back within normal tolerances since OS X 10.8.2 came out. Earlier versions of Mountain Lion had produced significant battery-drain reports, which Apple later ascribed to a faulty algorithm for calculating remaining battery life. Tests done by Electronista's independent testing lab continue to show that OS X Lion 10.7.3 had the best battery life on a variety of tested recent-model MacBook units, which hasn't yet been topped by Mountain Lion.