EDIT: As it turns out the quoted interpretation of serial numbers (below) is likely incorrect. Instead, to determine your build week please try this tool (thanks HiRez) to determine build week. The tool was made for older iphones but it may still be valid for IP4S? EDIT: If you are having battery issues please try Airplane Mode and putting your phone to sleep and observing the battery drainage. If it's significantly less drainage this is all very very likely just an iOS problem!