My battery frequently discharges if left for a period of time - why?

I have a 2010 Volkswagen Scirocco 2.0 TDI. After leaving it locked in garage for four weeks while on holiday, I found that the battery had discharged and the car wouldn't start. I have already had the car in the dealership to check the problem as the battery does seem to discharge with infrequent use, and they state there is not a problem. Have you any idea where the problem lies?

Asked on 29 September 2012 by AS, Solihull

Answered by Honest John
If you have a garage with a power supply, leave it hooked up to a battery conditioning trickle charger. But something you can check first is the 'see you home' delay on the interior light. These often malfunction and lead to battery drain. The solution is to switch the interior light off completely so it does not come on when you open a door.
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