If my thought about the problem is correct then where the battery maintainer is connected could possibly matter. Having 18 milliamps of current draw isn’t going to kill a good battery even after a week of being parked. It would be a real big help to know for sure if the battery is truly discharged after this problem occurs. So far I don’t think there is real evidence that shows the battery was discharged. Even the first tech stated there wasn’t any problem with the battery when he worked on it.
I have an 05 Carrera that had a similar problem. Security system, not driving a lot, and other stuff meant eventual replacement of the alternator. Off warranty of course. My car is a bit of a garge queen but does get driven. Bottom line - dead batteries, AND new alternator. Watch out. Go to websit for Zeppelin Works and send them an e-mail. CAnt hurt to see if you have the same problem I had.