I am now pretty sure the batteries are being shorted when it is turned on across the battery terminals there is a resistance if 0.5 ohms when not turned on and with the motors unplugged. I think that would make an instant current of nearly 50A so that could cause all that sparking. Any one know what kind of resistance there should be across the terminals? I imagine it should be very high as the only route for the electricity should by the LEDs which should have a high resistance.