Defender Devon 4x4 battery tray and optima blue top - terminal spacing

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Originally Posted by Dervish

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.

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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.