The current is needed for the starter motor ensure you have a good earth. Modern starter motors have a gear reduction and because of this draw half the current but give twice the turning torque!
As Arwyn says its all about the current draw and volt drop
Morgans 1934 MX, 1947 Series 1, 1956 +4 TR4, 2000 +4 T16
Triumph Herald 1969 13/60
Morris 1970
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