Yes! This is the info I was looking for.
I will go shopping for a switched mode regulator and a lipo pack.
I am looking at this lipopack from a local shop.
http://www.lipogigant.nl/a-147200/turnigy-1600mah-2s-20c/
This one should be ok. Do you agree?
@TeslaIaint:
Why are you using a rasberry pi and an arduino? Must be an interesting robot. Can you share? Or is it top secret? haha
It is just a project of mine. With a raspberry pi(running Debian Linux) connected I open up a whole world of features.
I am thinking of voice control, maybe add a webcam. My desktop-computer unlocks it self by facial recognition. Maybe i can implement something like that on the robot.
I have been programming linux for years now, but the electronics and Arduino stuff is new to me. I am progressing slowly, but ill get there. 
I really do appreciate all your support.
Jombo