Befuddled Battery?

[Driver8]

Hi all - I'm having an issue with the battery on my 2004 3.0i and I'm looking for advice and/or confirmation of my conclusions.

Problem: Car occasionally will start after sitting for a few days.

Symptoms: Lights come on and steering wheel/idiot lights/V-1 all do their thing, but there is not enough power to turn the starter. The solenoid clicks a few times but nothing more. A nice slow trickle charge revives the battery and keeps it alive as long as I drive the car every day or so. The problem got worse, though, and I replaced the battery with a NAPA-spec Exide 72-month battery. The problem reasserted itself yesterday after having the new battery installed for about two weeks. I installed it myself. Everything was done right and by the book. I have pretty much eliminated the battery itself as the source of the problem.

Potential Sources of Problem:

1) Undersized battery - Not likely, as it was one of two battery sizes listed for the X, both of which should be more than adequate. The case size is smaller than the OEM battery, but otherwise this should not be the source of the problem.

2) V-1 hookup - Not likely. It's attached to a switched power feed and goes out with the ignition.

3) BTUM - Not sure if this is powered full-time or not. I need to check the indicator light to see if it shows when ignition is off. Even if it stays on, honestly, how much power would a tiny blue LED indicator light draw?

4) Final Stage Resistor - Likely. I researched the issue earlier and this could be the culprit. While I cannot honestly say I've noticed the fan running with the ignition off, I can't say that I haven't, either.

5) Other Closed Circuit Issue - Possible. This one is beyond my abilities and since the X is still under warranty, I'd leave this one to the experts.

6) Alternator - Possible, but not likely. Assuming I drive the X every day, the battery will stay charged, a direct correlation between a good alternator and a battery that is being discharged when the ignition is off. Plus, I think a bad alternator would clearly manifest itself by allowing the battery to die while driving, but I could be wrong on that.

At this point, I think I have realistically eliminated all the DIY stuff that could be draining the battery. New battery. No V-1 lights when ignition is off. I'll double check the BTUM later today. I think it's a FSR or something not shutting off with the ignition. Any thoughts/comments/advice greatly appreciated!

Mike