It depends on the year of the van. Best way to check is take a voltage reading of the van battery then plug into the mains to see if the voltage increases. But remember it will not charge a flat van battery just keep it topped up
I'm pre-facelift, so that answers it - thanks. Got a jump start from campsite rather than paying for electric. Start battery has been on its way out for last few weeks but was just delaying the inevitable, i.e. buying a new one which I've done today!