I personally have never experienced battery life problems, although iOS 6 is running on an iPhone 4 And an iPad 3,1. 2 fairly recent devices. I'd say if you are experiencing battery problems on iOS 5.x.x I would not update to the iOS 6 betas as they are likely to make it worse. It's better to wait for the release in the fall when Apple has sorted all issues.
If your device is still under warranty, Apple will replace you battery free of charge, if it drops below 50% of its original capacity.
iPhone being under warranty would be the best option. You can take it in and they can run tests to see what is causing the battery drain. How long does your iPhone last? 1 day battery life is normal, at least for me. Also it depends on what you use your iPhone for. Listening to music and talking to people through FaceTime and just by calling them for a long time can cause the battery to drain faster.
As far as iOS 6 battery, I am not sure. But I'd suggest looking at everything you use and seeing what may cause the battery drain. 1 day battery life for me is excellent. I don't see anything wrong with that. I've heard others can go two days, but it really depends on what all you're using your iPhone for.