Hey Scooter, thanks for the information.
I called up my BMW dealership and they said it'd be an hour worth of labor to perform the "battery test procedure" they do. The guy recommended that I keep an eye on it for a few days before resorting to that though.
I don't have any aftermarket equipment in the car -- at least not yet. BMW said that I can't do the factory Sirius without replacing my head unit, so I'm going to have to go with one of those aftermarket plug and play units. Doh.
When I went out to lunch about an hour or so ago, the high drain warning came up again. However, when I left the restaurant and headed back to the office it didn't come back on. I'm thinking that might be a sign that everything is actually OK. I'm going to continue to keep an eye on it though, and if it comes to it I'll have to bring it into the dealership to have them take a look at it. It's $102/hr, but if they find something wrong they'll apply it toward the actual repair.
Now my next task is seeing about getting the factory navigation added in, if possible. heh.