Using Li-ion cells in LED flashlights safely

ven

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3.6v sbslider is not too low, that is the nominal voltage , also a good storage voltage(maybe 40-50% capacity. Most cells (variable) have a min voltage of 2.5-2.8v, so to play it a little safer, 3v minimum is a safe voltage to not go bellow(leaves a little room). But even then, if the voltage is bellow the min spec, for example it is 2.3v measured. As long as the cell has not been in this state for a period of time, it should charge up fine(being monitored to add) with minimal issue/potential damage. Most lights do have a built in LVP, also even without the LVP(low voltage protection) not many flashlights will power up at 3v, or certainly not in high modes. As with the load and voltage sag, it will blink or go out letting you know.

The little RCR123a cells(16340) do not have much capacity, usually 6-700mah in the tank(yours is 550mah ). Its a good idea to use the light and check cell voltage after a few uses. This way you will get an idea of how much use and where the voltage will roughly be. With my 16340 cells, i tend to top off back to 4.2v after use, as even a little use with higher levels(exl low and moon modes) does eat through the mah pretty quick. So by topping them back up to 4.2v, i know exactly where i am up to and good to go again. Now at 3.6v, you dont have that much left, certainly if your going to be attempting higher levels(if the light allow use at that V). If its for regular use, i would certainly carry a spare cell or 2 for the light. If you find your swapping cells out regular, then a compact 18650 light may work better for you. I love 16340 lights, the form for me is perfect for EDC uses, but not ideal for any decent duration. I would struggle in work for example, where a few hours of 200lm( ish as a variable) might be needed.

3.6v is a good place to top back up yes, but there are no safety issues at that voltage, nor going lower towards 3v. Maybe he was just giving you a large buffer to be extra safe, but i am sure the olight mentioned will not work bellow 3v.
 
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david.allie

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One other useful size you might want to mention was the 17500s; they're 1.5 CR123 cells, so you can stack 2 of them in a 3xCR123 light.

And that's where the 17500s shine -- 2 17500s at 4.2V starts at 8.4V, whereas 3 primaries @ 3V each start with 9V. Since the Li-ion hold up better under load, they work out great in most such applications.

I admit to being a n00b and know this is an old thread...

I’m not understanding how 2 17500s at 4.2V/each is better and “holds up better under load” than 3 CR123As at 3.0V/each. Would someone explain this to me?
 
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SilverFox

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Hello David.allie,

Welcome to CPF.

I believe you need to review the discharge charts for CR123 cells and 17500 cells. If the voltage remains higher on the 17500 cells, they should perform better.

Tom
 

SilverFox

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Hello Lumen aeternum,

The Streamlight 88047 ProTac HL 3 is another light that uses 3X CR123 cells.

Tom
 

xevious

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I have just one related question -- is it OK to recharge 2 x RCR123 cells in series? Even if a flashlight maker has produced a flashlight with recharging circuit primarily designed for 18650, but claims it can handle 2 x RCR123 for both output and recharging? I've never seen a dedicated charger support 2 x RCR123 in series, which of course makes sense because it can't detect individual cell status this way... which means one cell might end up overcharged while the other cell is still charging. So I'm presuming that 2 x RCR123 charging in a flashlight is not a good idea, even if a flashlight maker says it is possible.
 

SilverFox

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Hello Xevious,

If the cells are closely matched you can get away with charging in series without balancing for awhile.

One way to deal with this is to make it a practice of charging the R-CR123 cells externally in a charger and just know that if you need to charge inside the flashlight you do have that option.

Tom
 

AirTrainer

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If a fully-charged lithium battery (26650) sits idle for 2-4 months subsequent to charging, is there a safety concern? If the battery is sitting within a flashlight with the tail cap partially-unscrewed so as to open the flashlight's circuit, is there a safety concern? If there are two lithium batteries in series within the partially-unscrewed flashlight, is there a safety concern?

I haven't dipped my toes in the lithium battery 'pond' and I'm trying to decide if I'm going to bother. NiMH has been pretty low-maintenance compared to the impressions about lithium I've formed while reading this thread.
 

dragosios

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Open-circuit will not drain any battery, single or series.
Overall yes, lithium based ones have a higher energy to weight ratio, but they are more sensitive. Overcharging is a particular concern, but overdischarge will also render them unusable.
 
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