my project V6 car came with 2 Miata sized batteries. The PO installed the two because he wasn't getting enough amperage to the starter to turn over the engine. The Miata battery is about 2/3 the size of a "normal" sized car battery. I think if you are running heavier primary cable the smaller battery may work...... something that I am going to try with the next project.
I also recommend a rubber or plastic cover to go over what ever battery you opt for... they do bounce if not secured!!
I also recommend a rubber or plastic cover to go over what ever battery you opt for... they do bounce if not secured!!