8V not 9, but forget that, "better results" can be had with 6V in a good system, 4 gauge is 12V wire, 6V should be 1 ga or heavier, using 0 or 00 is really best, and make totally sure every place you connect ground cables to is clean shiny metal, and it's best to use an external tooth star washer on them, make it dig in so there's zero resistance at the connections
Bill
