I have a 2005 BMW 645ci

What is your question?

The battery goes dead if it isn't driven for only 2 weeks. I had the alternator checked by 2 different auto electricians and I'm told that the alternator is charging. Additionally, no ground shorts were found that would draw down the charge. My question is this--can an alternator or voltage regulator fail intermittently or do they work fine until they go?

How long has your 2005 BMW 645Ci had this problem?

6 months