An iOS update specifically designed to address celluar connectivity issues in the iPhone 4S is leaving many who use the phones struggling to get through the day on a single charge.

Monday's update, iOS 6.1.1, was intended to resolve an issue that could negatively impact cellular performance and reliability for the iPhone 4S. Instead, a number of 4S owners sounding off in various forum threads continue complaining of persistent battery drain issues. Although the problems do not appear to be as widespread as iOS 5's battery issues in late 2011, many users are complaining of overheating and unusually high battery loss.

"iOS 6 was seamless for my phone and I experienced no issues," one forum member wrote. "When I converted to 6.1, the battery retained about 30 percent of its usual lifespan– and overheats. 6.1.1 hasn't improved the situation."

Last week, U.K. carrier Vodafone warned its iPhone 4S-owning subscribers not to update to iOS 6.1 because of a known issue with connecting to 3G networks. These and other 4S owners also experienced battery issues with the update. Apple issued iOS 6.1.1 for iPhone 4S owners to address these problems. For some, the problem lies with having a linked Microsoft Exchange account to your mail and calendar. Deleting that account, rebooting, and then adding it back fixes the issue, according to Apple forum user Lawrence Finch. Apple is reportedly working with Microsoft to fix this, but also offers details on how to perform the above fix in its support forums.

iOS 6.1 has also revealed a new security bug that lets anyone bypass the lockscreen. How this vulnerability snuck into iOS is unclear, but the folks in Cupertino promise to set things right at some point.

"Apple takes user security very seriously," the company said in a statement. "We are aware of this issue, and will deliver a fix in a future software update."