This is my todolist for Raspberry PI development:

• make it battery driven
• use the GPIO pins to talk to my Arduino
• receive motion commands from Android phone via WIFI (start, stop, steer)
• send commands to Arduino
• receive ‘map’ updates from Arduino

I think I’m going to buy an external 5V accu, someting like this. Some of them have 2 output’s making it even beter for me, since I want to drive both a PI and an Arduino.