The servos are connected in parallel not in series!! ie if each servo requires 6v then you need a 6v battery irrespective of how many servo there are. Just the power rating of the battery (ie Amps) is important and the mAH will tell you how long the battery will last. These are basic electronic questions and not really to do with webbotlib
So you may need two batteries: one for the board (low power) and one for the servos (capable of delivery say 0.5A x the number of servos for the length of time you need mAH).
Then:
Battery 1 (anything between 7v and 12v):
+ -------------------- to the micro-controller
- --------------------- to the micro-controller
Battery 2 - for the servos (between 4.8V and 6v)
Each servo then has:-
+ -------------------------------> servo
- ---------------------------------> servo
signal from microcontroller ---> servo
And also connect the (-) of each battery together to give a common ground