The iPhone has a pretty good sized battery in there (according to iFixit, who took one apart), but the battery life of the iPhone making calls wasn't great; we measured it at 4 hours and 3 minutes in our first test and 5 hours and 1 minute in our second; we are running more tests now, and won't assign the iPhone a score until we have completed these tests.
That's comparable with the Helio Ocean, but is significantly shorter than the LG Prada and the N95. And it's less than half that of the BlackBerry 8800, which lasted over 10 hours. If you are thinking about this in terms of how long you can go without having to recharge, we wouldn't recommend going for more than a couple of days. And remember that the battery life will be even shorter if you are using the iPhone as a music or video player as well as making calls. For most users (such as commuters), we'd reccomend that you charge it every day.
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