slayer battery opinions

I have an extra mm sitting around with cc bec connected to it. I just ordered the motor the other day so its on its way. The tranny is using its 2 speed. It was the batteries I was undecided on.
I initially wanted to just run single 3s batteries in this setup as I really am not looking for back flipping power. The possibility of running the 3s in parallel will be there only if I really need the extra amperage, which is what I am unsure of.

In the previous post I meant running a single 3s or 4s battery; or running a pair of 2s batteries in series.