Assuming you have an LED flashlight that can safely handle either regular non-rechargeable 123's, or an 18650 or 2 rechargeable RCR123's, and you were to do a comparison test to see how long each battery type would last in that same flashlight on the same power setting, which battery or combo would last longest?
I would assume there are differences in current flow etc. from one type of battery to the next of the types listed above, so maybe the test might yield different results if the tests were done at different brightness settings. Maybe one type of battery would last longer with the light set on high, and another type might last longer with the light set on low(again, thats an assumption, as I dont yet fully understand all the electrical/current details). If my assumption is right, and there is a difference in how long a battery type will last vs. other types based on which brightness level the light is set on during the test, then hopefully someone can enlighten us on which battery type listed would last longest in the same light at different BASIC brightness settings of low, med, high.