Use the biggest wire you can. A short length of 8 won't hurt you too bad. The 6 AWG wire is usually used to minimize the amount of voltage drop between the batteries and the trolling motor. Most all breakers are 50 amps and that is higher than the current any motors draw when working properly. 8 AWG can handle 50 Amps no problem. If you don't want to splice (which could add less reliability and allow corrosion thus increasing resistance), try the Marinco 4 prongs they accept 6 AWG . If you are running straight 24V you connect the positive of one battery to the negative of the other, so in series you have 24 V. this is done in the receptacle not in the base that attaches to boat. dave