Thanks for your reply, but that looks just like a lupine micro charger with battery connectors?
What I am looking for, is to drive a pair of Bettys directly from the car battery.
I've actually bought one of these to see if I can put this together myself. http://www.ebay.co.uk/itm/271997712814
I've intentionally oversized the wattage of the DC-DC converter to make sure it has enough power for the Betty, but I'm probably going to test-run it on one of my Piko's first