The iPhone 5 is a great phone. I really was disappointed with the battery life. I would loose 20% of my battery over night. Throughout the day, I would end up needing to charge it more frequently. I figured out the culprits to be Google Voice and Facebook after following all of the tips on the other sites.
For Facebook, it would be best to logout when not using it to avoid frequent data usage Don't worry, it will still save the username and password for next use.
For Google Voice, it constantly uses data to check for new messages which will drain battery life. I ended up switching to my mobile number and experienced far better battery life.
Here are the commonly used tips floating around on the Internet that help immensely in addition to Facebook and Google Voice:
1. Set the screen brightness low as possible.
2. Turn off location services.
3. Disable as many notifications as possible.
4. Under mail preferences, turn off Fetch new data.
5.Change fetch interval to manual.
6. Disable LTE
7. Turn off Wireless
8. Turn off Bluetooth