Back in the "ancient times" that Zeke described there was the poor man's 6/12 volt battery, which was created by taking a standard 12 volt battery and running in a large sheet metal screw into the connecting bar between the third and fourth cells. The full 12 volts would just go to the starter and the rest of the car would be powered by an 8 ga wire connected to the 6 volt tap in the battery. Seemed to work quite well. I used it for several years on a 1951 Chevy with a 261. It was not easy to start on a cold day with just 6 volts. A 12 volt generator was required.
