The battery connections are part of a paralleled bus, so you can use one or two cables for each polarity. The choice comes down to the gauge of wire that you're using. The manual recommends 4/0 AWG or larger for a single 10ft run, but I've found that two runs of 2/0 AWG is a bit easier to move around. If you use one cable for positive, you'll want to use the same gauge and amount for the negative too.