the maxiumum recommended length from InovationFIRST is 25 ft. beyond that, if the robot goes crazy, it's not their problem. i've been content with using a 6 ft cable, for many uses. from diving the robot down the street (we were too lazy to carry it, and we had one battery that still had a somewhat usable charge
) to testing out the different systems on the bot. sure, i'd go for a longer one, but is it needed, not really. also, when you do connect cables together, the maximum length will go down, a lot.