1, you are lucky. My iPhone 5 needed to be exchanged by Apple because of the battery dying (which is pretty widely reported here in the MR forums too).
2, your 4S can only be 2.5 years old at most. That's not THAT much time.
My iPhone 3GS, purchased on release day (lined up for it for some 3-4 hours in the dawn) wasn't used for mapping either. Still, I needed to exchange its battery after 3 years of pretty light service because it wouldn't hold a charge for more than a few hours. (Fortunately, the given batch wasn't affected by the "swollen battery" syndrome depicted in my flickr shots.) Compared to that, my Nokia N95, which I (my wife) don't use less than the 3GS, is still going pretty strong with its original, 2007 battery.
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Too bad these kinds of benchmarks don't have any info on how the battery behaves after 1-2-3-4 years. In which Apple's batteries haven't been particularly strong. Even the ones not dying after half a year (many iPhone 5's, incl. mine so I have first-hand info on these bad batches) or swell (many iPhone 3G S') typically reduce their charge-keeping capability faster than, say, high-end Nokia models (e.g., the N95).