Smart phones use a lot of battery power. Plain and simple.
From what I hear, the iPhone has great battery life when compared to other smart phones. My friends Windows phone 7 gets 6 hours til it dies............And no, not 6 hours Usage..................Just 6 hours, and less with heavy usage.
I can have at least 10-15% after about 8-9 hours Usage.
My battery seems to drain about 10% for every 1.5 hours Usage (not stand by). heavy usage. Some day it is like randomly worse then that for some reason, but most of the time it is pretty good.
When i first got my iPhone i thought my battery life was so bad it pissed me off, until i realized that my iPhone had the best battery life out of my friends Droids, and Windows Phones.lol. It was then I realized that..............Well.......Smart Phones do so much of coarse the battery is not gonna last as long as any other phone, that is not a smart phone.lol. It just does more. Also uses less data then Android phones too.........So I have read lately.