A slightly more detailed list of specs reveal the GamePad's expected battery life and that it can be charged while in use.
Nintendo has released some slightly more detailed specifications for both the Wii U and its GamePad controller.
Height: About 1.8 Inches (not including protruding parts)
Length: About 6.8 Inches (not including protruding parts)
Depth: About 10.5 Inches (not including protruding parts)
Weight: about 1.5kg
CPU: IBM Multi-core Processor
GPU: Made by AMD, High Definition GPU based on AMD Radeon
Disk Drive: Slot loading. Runs Wii U and Wii game disks.
Controller Support: Wii U GamePad + up to four Wii controllers. [Editors Note: Nintendo announced at their Press Conference that up to two Wii U GamePads can be used at once]
Storage: Built-in Flash Memory, SD Cards and USB storage (USB Storage unspecified).
Visual Output: 1080p, 1080i, 720p, 480p, 480i.
Audio Output: PCM Linear 6 Channel output from HDMI, along with analog output.
Internet Connectivity: Wireless Lan (IEEE802.11b/g/n), or LAN adapter option.
USB: USB 2.0 x 4 (Two front & two rear)
Wii Compatibility: Wii Software and Peripherals with some exceptions.
Wii U GamePad
Vertical: About 5.3 Inches (not including protruding
Horizontal: About 10.2 Inches (not including protruding parts)
Width: About 1.6 Inches (not including protruding parts)
Weight: Roughly 500g
Screen: 6.2 Inches (16x9 aspect ratio), Touch screen.
Control Input: Touch screen, L&R Sticks, L&R Stick Buttons, D-Pad,A,B,X,Y,L,R,ZL,ZR, Plus & Minus, Accelerometer, Gyro Sensor, Geo Magnetic Sensor.
Other Inputs: Power Button, Home Button, Synchro Button, Audio Volume, TV Control Button.
Other Functions: Vibration, Inward-Facing Camera, Microphone, Sensor Bar. NFC functionality.
Wii U GamePad Stylus
Battery: Lasts 3-5 hours depending on brightness and other situations. Recharge time is 2.5 hours, can recharge while being used.