That s quite impressive.

http://www.apple.com/ipad/specs/

Battery and power⁴

• Built-in 25-watt-hour rechargeable lithium-polymer battery
• Up to 10 hours of surfing the web on Wi-Fi, watching video, or listening to music
• Up to 9 hours of surfing the web using 3G data network
• Charging via power adapter or USB to computer system

4.Testing conducted by Apple in March 2010 using preproduction iPad units and software. Testing consisted of full battery discharge while performing each of the following tasks: video playback, audio playback, and Internet browsing using Wi-Fi or 3G. Video content was a repeated 2-hour 23-minute movie purchased from the iTunes Store. Audio content was a playlist of 358 unique songs, consisting of a combination of songs imported from CDs using iTunes (128-Kbps AAC encoding) and songs purchased from the iTunes Store (256-Kbps AAC encoding). Internet over Wi-Fi and 3G tests were conducted using a closed network (for Wi-Fi only) and dedicated web and mail servers, browsing snapshot versions of 20 popular web pages, and receiving mail once an hour. All settings were default except: Wi-Fi was associated with a network (except for Internet browsing over 3G); the Wi-Fi feature Ask to Join Networks and Auto-Brightness were turned off. Battery life depends on device settings, usage, and many other factors. Battery tests are conducted using specific iPad units; actual results may vary.

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Xiaoyu Guan (Sam)
http://guanxiaoyu.blogspot.com