Just to know: if my flashlight indifferently uses as CR123A as 18650 batteries, what is better to use? That is is it better 2 CR123A or 1 18650 battery? What differences? THANKS
1*18650 as it’s rechargeable.
But CR123A too are rechargeable batteries.
Nope, CR123A’s are LiMnO2 primaries.
I usual uses 18650 because they contain much more energy, i.e. longer runtime.
The exception is lights that are stored away for emergency usage, there real CR123 batteries (not rechargeables) are best.
You tell me CR123A are not rechargeable but why are there charger that can charge CR123A batteries too? May be do I make a mistake?
CR123A are primaries, but there are also same-sized rechargeable batteries called RCR123 (also sometimes called "16340 batteries")
CR123 = primary cell
RCR123 or R123 or …. R = rechargeable
…….
Depend on the driver.
OK! They are the specs of my flashlight:
Operating voltage: 2.7V - 12.6V
It can be powered with 2 CR123A batteries, 2 RCR123A batteries, or 18650 li-ion battery.
I repeat my question: can I use the rechargeable RCR123A batteries? It seems that I can, therefore: is it better to use 2 RCR123A or 1 18650 rechargeable batteries?
2*RCR123A = 2*2.5 = 5 Watt-hours
1*18650 = 10+ Watt-hours
So 1*18650 will give you double (if not more) runtime comparing to two RCR123A’s
THANK!!
My light is similar in that it can use 2xRCR123 or one 18650 for rechargeables. Often the higher voltage of the 2xRCR123 allows brighter maximum output, but if you don’t mind losing a few lumens in exchange for much longer runtime, then the 18650 is the better option. I use 18650 cells exclusively in my light for the added runtime (over 4x longer), and using single cells prevents any imbalance between multiple cell configurations.
It’s better to use 18650 , because out of a flashlight you want as much runtime as you can get …
1 X 18650 , let’s say with a minimum of 2500 mah real capacity -> 3.7 V x 2500 mAh = 9,250 Wh
2 X RCR123 ( 16340 ) , with tipical capacity of ~ 650 mah - 3.7 V x 650 mAh x 2 = 4,810 Wh
==> you have almoast 2 times more juice from one 18650 , than 2 X RCR123
Uh, JustFit, power is measured in Watts, mAh is measurment unit of capacity.
Also, 3.7V*2.5Ah = 9.25Wh, not 9.25W. Don’t confuse people :Р
Edit: thanks for correcting it :Р
right , and done …, thank you! 
More - at higher load RCR123 capacity decreases and actual runtime is about three times shorter than with 1x18650.
18650 is best IMHO, if nothing other than for ease of field replacement and backup carry.
The only reason I can see 2xRCR123 being advantageous is if the light has flatter regulation at 8.4V than 4.2V. Not all lights are regulated at 4.2V.
I’d like to buy Genuine Panasonic 18650 batteries by DXDealextreme but in their web page i read “SKU” 121444. I don’t like much this writing. What does it mean? May be they are not original? The link is: http://www.dealextreme.com/p/genuine-panasonic-18650-3100mah-rechargeable-battery-with-protection-board-green-pair-121444?item=2
Then: are they protected batteries?
Thanks for your news.
SKU = Stock Keeping Unit, basically ‘alternative’ for UPC barcodes. It’s nothing you should worry about.
I have just noticed they are not protected batteries. I read “with Protection Board”, this is a different thing. Right?