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shiftd said:
if around 30 min runtime is what you considered reasonably well, then yeah. I think rechargeable 123 can handle up to 30 min of burn time. Assuming your 5W has 7V Vf at 500 mA, and 80% efficiency, 3.7V input from liion, your converter will draw about 760 mA from the battery.
Assuming the battery has 600 mAH (rechargeable liion 123 is rated at that cap), take at least half of the cap as lower bound and you get 300 / 760 = 23 minutes.
Well, it clearly shows how important it is to get low Vf lux5W. hope it helps.
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I know little about calculating current but two different Lux-V BB750's that I have draw 1.8A measured from a JSB123 protected cell or a Pila 168S. I did some runtimes and if I remember correctly, it was 12 minutes! The protected JSB123 are just under 500mAh measured with a CBA from West Moutain Radio.