An 8 volt battery is not necessary if your system has clean connections and at least a 2-00 positive and ground cables. Once you get that done, you adjust the third brush on the generator to 0 amps on the amp meter at idle with the lights and heater blower on. You should have around 7.5 volts on the output of the generator.
I am using a 6 volt Optima battery in my '36 GMC and have not had problem one.
