I am also wondering if this "resistor" is the real culprit or just something to get you into the shop so they can fix something they'd rather not tell you about.
Mine was built 12/2004 and I did not get a letter today. Maybe tomorrow....
If I start asking around, and they tell me not to worry, it was just a weather balloon... I'm going to be even more suspicious!
Somebody watch when they do it if you can.
I doubt they will plug anything into "the battery".
Most likely they will connect to the OBD plug under the steering wheel... or perhaps... but less likely, under the hood.