I have an almost new Alfa Romeo 159 TI. I have no complaints with the car other than a battery problem. There are occasions when I have to attend conferences abroad, leaving the car in the open air car park for a period of one or two weeks. On my return I cannot start the car without garage assistance. The car was checked out by my garage who were unable to trace any fault, so a new battery was fitted. The car worked fine without any further problem until this month. I parked the car at Heathrow on 26 July and returned on 6 August. The battery was again flat. Nothing had been left on. Once started, the car gave no further problems. Any idea what the problem is?