Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
3 Tips To Save Your Battery On Your iPhone 5
People always are disappointed with the battery life of their iPhones so below we have put together a list of changes you can apply in your settings which will increase your battery life. The majority of these settings changes will work on all of your iOS devices.
Turn Data Push Off
Find it in Settings -> Mail, Contacts, Calendar -> Fetch New Data -> Slide to Off
Turn Bluetooth Off
Find it in Settings -> General -> Bluetooth -> Move Slider to Off
Do not expect to see your battery life double or improve a massive extent but doing some or all of the above will help save them extra few percent which you may just need.