car battery draining after 2 days if hardly used

I have had issues with my convenience control unit and the VW garage said I had a leak and this unit was wet, They cleaned it out and dried out the unit, Everything worked fine after this, Before this happened I had a new battery fitted as it kept running out of charge. This was all 2 months ago now. But recently the battery is dying again. It has been in the garage and they say the battery is fine, They think it could be the alternator or a belt attached to this, They want to replace the belt first to see if this solves the problem.

Could it be the convenience control unit causing the battery to drain.

Many Thanks