Apple has released the latest iOS version 6.1.3 earlier this month which fixes critical vulnerability. Unfortunately, it seems that when Apple fixes something, it breaks something else. An increasing number of users are reporting faster battery drain when using WiFi and Bluetooth connectivity than before.
According by Apple Support Communities user Markbob917, there is a possible fix for it. Be advised that this is no an official fix and might not work for all users.
1. Visit the iCloud section in the iOS Settings and toggle all services to OFF, making sure you save your content (to iPhone, iTunes backup etc.).
2. Do this for each email account but make sure you select to keep data on iPhone (not delete it).
3. Do a hard reset by holding the Home button and the Sleep/Wake button for 10 seconds
4. Wait for the phone to reboot, then go back into the Settings app, then access Mail and turn account back ON.