As Wayne indicated the Auto Stop Start battery was indeed in/behind the passenger foot well, when I said All be it American auto mechanic, meaning it was a left hand drive car he was showing, but still strange the main battery and the auxiliary are on the same side, Benz Europe I guess. It is a Mercedes Labelled battery but from what I can gather there are two types, identification escape at the moment that don't and cant readily be charged by a bog standard 12v charger > your thoughts appreciated.