Make sure the battery is in a good state of charge and LF window is down . With all accessories turned off and battery negative cable disconnected at negative battery post . Turn the ignition key to on , then fan the area around the battery to disperse any flammable hydrogen gasses before reattaching the negative battery cable (with ignition key on) because it will spark.! Often seems to help keep security features in a sort of valet mode having ignition key in the on position before attaching negative cable . At your own risk, even with eye protection be very careful with sparks around batteries!