A car battery has a lot of amps available amps. It is harder to create an arc with 12dc due to the lower voltage.
12volts dc will kill you. I saw a guy while i was in the army lean over the battery compartment and his dogtags contacted the battery terminals. It flash fried the tags to his neck. He was blinded for a week and got a medical discharge from the army because it screwed up his neck. We medivaced him to the hospital.