This is something I built for my son a while back. Basically I stuffed a raspberry pi running retropie into an nes shell and put a 7 inch hdmi screen in it as well. I was able to wire the controllers using the pi’s gpio and use the controllers for playing the games through emulators. I also used the original power/reset and led on the front of the console. It had 2 usb ports for mouse and keyboard, WiFi and Ethernet connection.

Here my original post on the petrock blog forums

http://blog.petrockblock.com/forums/topic/prepare-yourselves-i-think-its-original-nesberrypi-portable/

Here are some pictures of the insides

This is the 7 inch LCD screen, battery, speaker and charger port.

This is the raspberry pi with all of the necessary wires. Top left is the controller ports connected to the pi’s gpio. There is also a powered 4 port usb hub.

These are the usb ports located on the back where the power connector used to be. The small hole is the charger port.

Here is me enjoying a game of donkey Kong classics.

Last but not least here is a video of my son Johnathan playing his favorite game at the park. He loved it.