Small tip. If you are worried about input voltage. I often use cheap switching BEC's from e.g. Hobbyking. They will convert varying input voltage (6-26 volt) to constant 5 or 6 volt output. Also ensures servos run constant speed.

I use LiPo's for most of my hobby projects and have a nice flat 2S 1000mah for my Nybble. Instead of battery compartments, what works well is just a bit of self-adhesive velcro on Nybble and battery. Easy low cost solution and you can even move battery a bit around if you want to play with center of gravity.

Have V0_1 of the board. Had several issues with crashes and resets. After soldering path 1 all is working.