Batteries for $50 robot

[osnap]

I'm planning on making the $50 robot and ordered these for the RC battery pack:

http://servocity.com/html/6_0v_1450mah_nimh_battery.html

Now for my extremely noobish question:
I just noticed the battery pack has 3 wires... what is the third/gray one for?

Any input is appreciated, thanks!

[Dr_Worm]

I believe that is for the ground. 

if you look at the upper right of the 50 dollar robot diagram you should see it:  http://www.societyofrobots.com/images/sbs_avr_schematic.png

[Admin]

that white wire doesn't do anything (measure it with a multimeter to check)

its just cheaper to manufacture 10,000 three wire plugs than 5,000 two wire (for batteries) and 5,000 three wire (for servos) . . . its a mass manufacture thing.

[david_or_johnny]

Yup! Admin is right.

[osnap]

oh okay, thanks