I want to ask what is the average life of your iPhone 4 running iOS 5, with Wifi turn on, and what you are doing is just surfing through Safari. I'm getting 1 percent decrease every 3 minutes.
When actively browsing, that's not unusual. 1% every three minutes is 5 hours, which is expected if you've got the display on and using the wifi for browsing.
If it dropped 1% every three minutes with the display off, then you're likely running a background process that uses wifi and/or the GPS (turn by turn directions, running tracker, online streaming music, etc).