I was on the road for a bit the other day, and when I left home at noon, my iPhone's battery was about 95% full. About 4 hours later, I saw it was down to about 25%, and I wondered what it could have been doing to deplete the battery so much. I thought of the usual culprits, like brightness (it's not at the maximum), Bluetooth (it seems well behaved with iOS 6, going in standby mode when not in use), or push email. Then I looked at which apps were open. I quit them all, including Skype. An hour later, my battery had only dropped another 5%.
When I came home, I did some googling, thinking it could be Skype, or it could be another app. I came across a Skype forum post where someone said they lost 70% in four hours, just like me. There were no other apps running that would have been keeping a connection open, so it's safe to say - given the vast number of people who have commented on the relationship between Skype and poor battery life - that there is a link.
So, if you use Skype, and see bad battery life on your iPhone, try quitting the app and see if this improves things. I haven't done any scientific testing, but there seem to be enough people who have this problem to suggest that Skype may be the culprit.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20130124092557493