. . . . The battery needs to have enough energy in it for the alternator to start working. If the battery has at least 5 volts that should be enough for the alternator to put out at least 10 or 11 volts which will allow the ECU, Fuel Pump, Injectors, and Ignition System to operate. If the battery is completely dead the car won't bump start.
GOD Bless and Thanks,