2002 Volkswagen Eurovan Starting

Six months ago, we experienced difficulty starting our '02 Eurovan. In turning the ignition key to start the engine, we would hear a double click from the engine compartment on the passenger side, then nothing. The engine would not start. It would repeat as we turned the key until the engine eventually started. The problem grew progressively worst. We took the Eurovan to our independent VW repair and they said our original battery was low and needed to be replaced. We replaced it and the problem disappeared. Here we are six months later and the same identical problem is back with a newer, fully charged battery. What do you suspect the problem might be this time?