Woah, Woah! Headway cells are lifep04 chemistry. They are 3.65v max so 4 in series is 14.6v max. Your way over charging these. Also, you should build an insulated box of some kind so the metal ends of the busbars don't poke through the carpet and short out.
How did you secure the bank to the floor of your vehicle? I'm debating on how best to do so with mine. Either a strap type setup or bolt mounted.... Toying with ideas.
