Battery draining quickly is often associated with bad software. Hook your phone up to iTunes and create a backup, sync all of your content, transfer purchases, import pictures, etc. Once doing that, restore your phone as a new device. Do not put the backup back on the device because if it is software related, it would essentially put the same issue on the phone. Sync your content back over and test the issue. If the battery life is still terrible, then it's a hardware issue and your phone would need to be replaced.
The battery drain issue started when I updated my iphone 4 to the IOS 6.1.2.
The battery will go from 100% to 0% in about 3 hours !!!
I called Apple support and they told me that they are not aware of an issue affecting the battery with the latest update. They did a diagnostic test on my iphone and found that my battery is healthy. Then then recommended that I backup my iphone, restore the factory settings and recover after that. In other words, delete everything off my iphone and reinstall everything all over again. I waisted a couple of hours doing that and .....I still have the issue of the battery drain.
I finally discovered the problem, and thus the solution!
To solve this issue, do the following:
Settings ---> Mail, Contacts, Calendars --->Fetch New Data ---> Advanced
Now click on your hotmail account or your company email account (anything in that folder other than yahoo, gmail or aol),
Change the setting from Push to Fetch !!!
And Viola ! Problem will be solved !
The problem seems to be that the mail exchange (i.e. microsoft, hotmail...etc) keeps checking and pushing emails from the exchange server every second (continiousely) and this is causing the battery to drain.When you change the setting to Fetch, then emails will start downloading every 15 min; but at least your battery will hold charge as it is supposed to do, until Apple comes up with 6.1.3 that hopefully will fix this issue.
Good luck. Hope this works out for you folks hence it sure did work for me this morning and it sure feels great.