Originally Posted By: dougwalkabout
Yes, the word is that for some LED lights put it between the endcap spring and battery

That's the best way. Reversing one of the batteries even in a 2 battery light still leave room for electrical potential, which will drain the batteries if the switch fail or leak (that happens too due to a hidden defect). All cells are slightly different in voltage and resistance.

Art_in_FL
I'm second to your recommendation.
Though, for a small kit (like EDC) it is impractical to keep batteries and empty flashlight separately. Except if you consider to stuff the latter with something precious for protection...