Direct current is dangerous at high amps, in conventional application of a car battery if you cross the terminals with a conductor the battery can explode. The batteries in an electric car would have to protected in some manner to prevent a direct circuit between terminals or it could be dangerous equal to exploding gas tank.

You can connect batteries together noting the amps of each battery and use them to weld with by connecting welding terminals to the neg-positive terminals without damaging the batteries but if you complete a hard circuit heat builds up rapidly resulting in explosion if the batteries have a full charge.