Apple said the top surface of the touch-screen phone, due to ship on June 29 and priced at about $500 to $600, has also been upgraded to optical-quality glass from plastic, making it more resistant to scratches.
AT&T, the biggest U.S. wireless provider, has an exclusive agreement to sell the phone in the United States for at least two years. The company has said that more than a million people have inquired about the phone via e-mail.
But wireless experts have questioned whether Apple's first phone, built off the success of its iPod music and video player, will live up to the industry hype ahead of its launch.
"It all depends what (consumers) use it for but I think it would make quite a bit of difference ... versus traditional smartphone talk times," Yankee Group analyst Lauren Cotes said, comparing the iPhone's eight hours of talk time to rival devices with four or five hours.
The iPhone battery cannot be easily removed, unlike those of traditional cell phones, so power efficiency is an even more important feature of the device, Cotes said.
"They're definitely listening to their customers' initial concerns about the iPhone," she said.
Shaw Wu of American Technology Research questioned if the phone would live up to its claims.
"We hope those times are accurate, but our sources have indicated iPhone's active use battery life may be closer to around 4-5 hours for heavy use, similar to other smart phones," Wu said in a note to clients. He did not name his source.
Apple shares rose $3.79, or 3.2 percent, to $124.29 on Nasdaq.
Manufacturers are battling to increase the battery life of cell phones, as constant communication with radio broadcast towers tends to drain power more quickly than unconnected consumer electronics devices.
Smart phones like the iPhone also need lots of power as they also aim to handle Web browsing, personal data storage and music and video playback.
Apple said its battery claims are dependent upon specific configurations and "many other factors." It did not give further details on the longer battery life.
Sony Ericsson, a venture of Sony and Ericsson, has touted a talk time of up to 9 hours for some of its Walkman music-playing phone models.
A rival music player phone from Samsung Electronics, the Upstage, has a battery life of up to 6.3 hours, according to Sprint Nextel, which sells the phone.
The BlackJack, another Samsung phone, has talk time of up to five and a half hours, according to AT&T, which sells the phone.
Apple said all told, the iPhone can support up to eight hours of talk time, seven hours of video playback or 24 hours of audio playback. The device also retains its charge while not in use for more than 10 days in standby mode.
By comparison, the Curve from Research In Motion has a talk-time of up to four hours, but has a standby power of up to 17 days, according to AT&T's Web site.