Range Rover sport 2011 3.0 TDV6

Hi I have a Range Rover sport 3.0 TDV6 2011 I have no crank or turn over have replaced starter motor and battery and have checked all the relevant fuses and connections but I have been able to start the car by putting a battery on the floor with positive and negative wires from starter motor to battery and done the screw driver test and the car will start but when on the cars battery there is only lights on dash when I push button to start the car the ignition just goes off is there anyone out there that can help