Despite Apple’s claims that the iPhone 4S has better battery life than its predecessors, it has roughly 33% less standby time than the iPhone 4 and iPhone 3GS.
This means that when you’re not using your iPhone 4S, you’re draining battery a whole lot quicker than with previous iPhone models.
The data comes straight from Apple’s iPhone comparison site, which says that the iPhone 4S has 200 hours of standby time, while the iPhone 4 and iPhone 3GS have 300 hours of standby time.
Battery life is one of those things you don’t notice until you don’t have it anymore. But you can always follow Official Apple’s iPhone battery power saving tips.