Thanks for the share reppans, the reason i mentioned such was because my setup with the two unprotected 14500's on my Turbo X, I used it until it showed signs of low voltage (when the light cant hit turbo or high mode) So I took out my cells, measured the one at the back, it was still about 3.6 to 3.9 volts, the forward cell had only 1-volt left. Fortunately, i was able to charge it back to full health. (phew!)
On its original 2xCR123 tube, I have killed three RCR123's because the forward cell had dropped to zero. Normally I leave my light on overnight in moonlight mode, one morning, I noticed my Turbo X was off already, to my dismay, the voltage of one was about 2 volts (DOH!) and the 1st one was zero (translated: dead cell).
Learning from that, since then, when I run my Turbo X head on its original body, i use a protected 17670 cell. No more dead cells!
I still run the Turbo Head with two 14500's sometimes when I feel like it, at least its nice to know that there's that option should there be any need to run it that way.
How I just wish FourSevens would bring back their 18650 tubes. In this day and age, 18650's are the way to go when it comes to rechargeable lighting over longer periods compared to the smaller cells.