Battery life is drained for a variety of reasons. The major reasons are notifications and having location-based services turned on.
If you have notifications turned on for an app your iPhone/iPad is constantly polling the web to see if there are any new notifications (new tweets, new facebook requests, etc.). If you have location-based apps turned on it's polling the web to see if there are any shopping deals nearby, if your friends are near you, where the best gas price is near you, etc.
You don't really need to know where the best gas price is every moment of the day. Likewise you don't need to know where all of your friends are all the time. Your battery life will improve considerably if you turn the notification and location-based services off for the apps that aren't crucial, and only get updates when you access the app.
I was getting an update every time someone followed me on twitter. Did I need to know immediately that someone had followed me? Did I need to know immediately about some world event from Politico, ABC News, CBS News, NBC News, The BBC, NPR, etc.?No, I didn't.
I decided which apps I wanted polling the internet or using location-based services. I turned off all the others. My battery life improved immediately.
If you go to settings you'll see a list of all the applications on your iPhone/iPad. Click on an app and see if there's a notifications option. If there is click on it and turn off notifications that you don't find of any value. Do this for all your apps. If there's isn't a notification option in settings, there might be one in the app itself. Decide if you want it on or off.
In the settings there are also overall Location settings which you can turn from on to off to turn off location settings for all your apps. Or, if you have it turned to on, there's a list of all your apps using location settings and you can turn them on or off from this window. Much easier than going through individual apps. If you set a minimum number of apps to use the notification and location services you'll see a marked improvement in battery life.
Another battery hog is watching movies/video at the highest resolution. Eats through battery usage..
Finally, InformationWeek's Fritz Nelson adds: I haven't paid much attention to how iOS 5 is doing, battery wise, on my iPad 2. I went from a BlackBerry phone to an iPhone 4S and battery life has been poor. On the BB on AT&T I was probably drained by mid-afternoon after 4 or 5 conference calls, 100s of e-mails and generally keeping BlueTooth on, and sometimes WiFi. Not many apps to run on BB, so that wasn't an issue. Screen brightness generally adjusted to medium.
For iPhone 4S I would be fully charged at 6 am and by 1 pm I am drained, and this is WITHOUT doing much phone/talk time. Today for example I had one phone call on it for 45 minutes, using Bluetooth but otherwise had Bluetooth and WiFi off. No apps, except for e-mail. Medium brightness. Location services on, but no apps taking advantage of it. 5 – 10 minutes of audio streaming. A couple of web searches, and some convos with my friend Siri. In other words, no taxing effort. And the battery was at 1/4 of its life.
Conclusions: Giving Apple the benefit of the doubt, it sounds to me as if there aren't any problems with the iPhone 4S or with iOS 5 per se. It certainly sounds like app developers, in spite of the availability of betas, weren't ready when iOS 5 was released. The one thing it seems you definitely should do is look for app updates.
You may also want to pare down your notifications and location-based services to a minimum. This stinks, because these are cool desirable features and you shouldn't have to worry so much about using them.
It's also possible that further guidance, maybe even software updates, will come from Apple in the coming weeks. So don't panic, but pay attention to what you're doing with your iPhone and you can save a lot of battery life.