Amazon.jp has listed the Battery Pack 4, revealing some details and images for the PS4 accessory. You can check out the photos for the Game Tech product below this paragraph.
The Battery Pack 4 adds an additional 1000mAh battery for the DualShock 4. This should double the batter life of the gamepad, letting gamers play for around 10 to 20 hours (the amount varies based on the usage environment) per full charge.
The biggest complaint regarding the DualShock 4 has been its relatively short battery life. This is apparently due to the internal LED light in addition to the touch pad. So, if you are looking for a way to cut down of recharging the controller, you may want to check out the Game Tech Battery Pack 4 if you are in Japan. In North America, you can also take a look at the Nyko Power Pack with this page on Amazon.com.