brushed hv setup questions

[Thunderbruiser]

Ok i've decided to try and make a homemade 13cell(15.6v) 3700mah battery for my rustler so i could drag race around my home. I've wired them up but they're slow about as fast as when i ran the truck on 7 cells

did i wire them wrong?

I connected the batteries by stacking them on top 6 cell pack on bottom,7 cell hump on top and then I made a connection negative to negative, and positive to positive both front and rear and then left the 7 cell hump the way it was..my question is is that correct or wrong?

illustration of my wiring job:



front of pack



rear of pack