How to start a car with a flat battery using jump leads. I have seen these directions in more than one user's handbook, across various makes.


Assuming both cars have negative battery earthing (not that I assume anything, especially if there is the likes of a Morris Minor involved):

1. Connect positive of one car to the positive of the other.

• Connect the negative of the car with the good battery to some convenient point on the engine block of the car with the flat battery. 

No explanation given of why do it this way. It works. But it is not exactly an easy instruction to remember if the handbook is not available. My guess is that the vast majority of motorists simply connect directly to both battery terminals, red to red and black to black, which works perfectly well in all circumstances.


So why connect to the engine block instead of the battery terminal?  I figured out that this might give a lower resistance path on the "jump" circuit by eliminating the resistance in the connection from the battery negative to the earthing point and providing a more-direct path to the starter motor. But this resistance would be very low any way - far less than the resistance in the jump leads.


Any better suggestions, anybody?