Quote Originally Posted by Dervish View Post
I would however cable tie some thin plastic over that battery hold down bar to prevent shorting it when you drop a spanner on it.
Sage advice. I once nearly ringbarked my wrist when I shorted a spanner to earth through my watch band. Surprising how much current a starting battery can deliver.

That's the point here though. Amps vs volts. You need volts to arc, hence the voltage in petrol ignition systems. I think the rule of thumb was 10,000 volts to jump 1cm. 12 volts isn't jumping anywhere.