VW Jetta - Power Problems

My niece has a 2005 VW Jetta. It has had 2 alternators and 3 batteries replaced - all within 2 weeks. The mechanic (very trusted) can’t seem to find the problem that is causing her car to die if it sits more than a few hours. Any ideas?

Isn’t this car still under warranty? Take it to a VW dealer and let them fix it.

Sorry, I just found out that her car is a 2003, out of warranty

What specify is happening to the alternators and batteries?  

I suspect the alternators may have been rebuilds and depending on who rebuilt them, should always be suspect.  The ones from the discount auto parts stores that come with a warranty are them least reliable.  While batteries can be bad, they are far more likely to be OK.  A bad alternator can kill a battery.