Sorry to hear about your problems. Unfortunatly, these cars do have lots of parts that seem to expire around the 90-100k mile mark (please tell me yours has at least that many miles). I think in spite of the repairs the car is a great value.
I just replaced my own air mass sensor ($250 from MercedesShop.com). While the broken one was in the car the wildly fluctuatng idle caused the "low batt" warning but I have not had any further electrical problems. I know it's obvious but how old is your battery? I'm sure the dealer would've checked it before installing the SECOND alternator. If they are "load testing" it they may have killed it. (I replaced mine with an Optima which cost about the same as the MB battery but is lighter and has superior technology). At least they are standing behind their work by replacing the faulty alternator.
You can save a WHOLE lot of money by searching this board to diagnose the problem and then ordering parts from PartsShop or Fastlane. the service is nothing short of perfect in my experience.
RIP "Betsy" (Oo=*=oO)
'96 E 3 2 0 (W 2 1 0) M 1 0 4 (Totalled)
Spaces in sig so as not to screw up the SEARCH; every time someone searches for that MB they don't want my sig!
2004 Audi A8L
'98 VW Passat 1.8T 5M
'87 Alfa Romeo Milano 2.5L 5M
'67 Impala convertible, 327cid