How long should an iPhone battery last?

I have an iPhone 4s that I bought this past January. My battery lasts roughly 3 and a half days with the odd couple of minutes of phone calls. And to check my phone periodically. Now is this normal for an iPhone battery when left on or should it be lasting longer?

I think that is an example of good battery life. My 4S was lasting around 2 and a half days between charges and I have no voice plan (hearing impaired).