I know the HFL module can cause battery drain but I noticed a glow in my car recently when I was in the garage late one night. Turns out the green LED on the overhead, interior lights switch stays on. Could this be another batt drain issue?

On my 06 RL the little green LED stays on if I select it so that the cabin lights come on when opening the doors. I never noticed this before. Does this happen on your RL? I haven't read that this is a problem but it has to drain the battery. Is this a know issue? I didn't find any mention using search.

 

Can't speak specifically to your RL but that is how it works on my 2010 TL.

 

Yes, that green LED stays on.

 

So a small sample but it seems this normal and a bad thing. I doubt the single LED has much of a draw but it does draw something. It was enough to notice in my dark garage. If any of you know how to measure the draw it would be interesting to know.

 

There's always a small amount of parasitic draw in every car - Radio memory, ECU memory, clock, flashing immobiliser light, etc. etc.
It's perfectly normal, but it should be a low enough draw to last months on the battery alone...