I know that this is out of context for this section but the old Nite Ize 3-LED drop-in conversion for the Mini-Maglites worked better than any other battery vampire that I've ever tried. I have a few cut down Mini-Maglites where that drop-in was still producing light well after the batteries have leaked inside the flashlight that it was installed in. I'm sure that it can be modified to drain just about anything with 3V or lower output.
It was intended to be used with the Mini-Maglites so 2AA. I ran one in a cut down single AA Mini-Mag and that one ran the cell down to the point that the battery had thoroughly leaked inside the light. If you are creative you can modify the drop-in to be used with other cells.