CR123a LITHIUM batteries are used in Fenix torches, Surefire, Wolfeyes, Ultrafire, the list goes on. They are 3volt and usually are 1300mAh (Milliamps)
Please understand I do not wish to patronise, however:
V for Voltage = Power (or if you like the STRENGTH of a Battery.)
mAh for Milliamps = Runtime (or STAMINA of a battery)
Now then, the Power (V) is Important, that is what the device, in this case an LED Torch needs to make it work.
A torch that uses 2 x CR123a batteries is using 2 x 3V Cells (another name for battery) the Total Voltage then is... 6V, correct.
Now if these batteries are rated at 1300mAh each,, the total in mAh is? 2600mAh, right.
WHAT IS THE POINT?
I'm getting there...
Rechargable CR123a are NOT LITHIUM, they are Lithium Ion or Li-Ion or In some cases NiMh, Nickel Metal Hydride.
These are made as 3V batteries, but the MILLIAMPS are less, usually 600 - 680mAh.
* * Side Note * *
There are some sellers that will claim their batteries have a much higher mAh rating. ie: 3v battery 900mAh
I happen to know TWO things for a FACT
1/ It is Very, VERY Difficult to determine the Milliamps of a Battery, you can't do it with a Multi Tester. Though you can get a rough idea by using the energy in the battery while monitoring the power drain and doing some Mathmatical Wizardry that is far beyond my feeble capabilities.
So you just have to take their word for it, if they say it's 900mAh, it must be. Right?
2/ If a Seller Buys enough batteries (5k minimum) He can have his Own Lables printed for the battery. His Very Own Brand of Battery.
That's Cool Huh.
NOT ONLY THAT... He can have whatever mAh printed on their he likes, after all, who can check it?
I'm not kidding. If I wanted to sell my batteries and claim they were 900mAh, I could. As long as there is nothing to contradict me on the packaging, I'd get away with it.
Most folks would be quite happy with what they had, only the choosen Few would check the runtime of the battery and may come to a conclusion that "Its Not Very Good"
But that woldn't stop the joyful masses spending their hard earned cash on this 900mAh Super Battery now would it.
HANG ON A MINUTE...
Am I saying that no such battery exsists? Well, I havn't seen one made by a Reputable Manufacturer, yet. That doesnt mean they don't exsist. BUYER BEWARE is all I'm Saying :o)
* * Side Note End * *
The brightness of a Torch is going to be the same as the Lithium Cells, but the runtime will be less, over half infact.
This is a bit of a pain, BUT by using rechargeables, you are helping to save the Planet, and your Bank Balance.
SO WHAT ABOUT these 3.7v Lithium Ion (Li-Ion) Batteries? ARE THEY BETTER for my Torch?
NO, not unless your torch can handle the extra Voltage.
Digital type torches (Fenix P3D for example) do not like having More voltage run through them than they are designed for. A normal RCR123a (yep, the R is for Rechargeable) rates at 3v BUT may sometime Spike upto 3.7V, especially when they run a little hot.
Sometimes regular Xenon type bulbs don't like the extra power and may blow the lamp.
A 3.7V Li-ion may Spike upto 4.4V when running hot (or freshly charged), do you see where I am finally going with this?
The extra Voltage (2 x 4.4v = 8.8v) is going to make mincemeat of your Digital Torch, a definatly blow that expensive Xenon bulb. So guess what, you're going to be buying another one very soon.
Rechargeable Li-ions do work fine with some Torches and Flashlights, just make sure YOU READ THE MANUFACTURERS INSTRUCTIONS, you know that little piece of paper that comes with the torch that you throw away without reading. It usually says on there "If you damage the torch using incorrect batteries, tough luck bucco" or words to that effect.
Not enough Voltage means it wont work properly.
Too Much Voltage means it Won't Work Again!
And if in doubt, ASK!
The wrong batteries really will bugger up your kit.