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Battery Information

Batteries are not so simple. Once you know a lot about them, they seem simple... but learning about them is difficult at best.

To keep it simple, when selecting a flashlight choose an AA/AAA based flashlight if all that matters is that it is a flashlight and you can easily pick up batteries in the store. It is still cheapest to get Ni-MH batteries and a charger for primary use in the flashlight, but Alkaline or, better yet, Lithium can be used when recharging the Ni-MH is not possible at the time. Some can be as big as a C or D cell based flashlight and use 6-8 batteries to get more output than the C/D cell flashlights... but half the runtime.

C and D cell flashlights are going out of style so they aren't being updated. With batteries available in Ni-MH and Alkaline versions still availble in store, these are still good flashlights for output, runtime and throw distance.

The best option for performance comes from 18650 Li-Ion based flashlights. A flashlight running on two 18650 batteries can have far higher output than a flashlight with eight AA batteries... or drop the 18650 to a similar output and have a longer runtime than the AA based flashlight. The draw back is that if the 18650 batteries run out and there are none charged on hand, the substitute batteries are harder to find, CR123A (Lithium), and two are needed for each 18650 being replaced.

A flashlight running on CR123A batteries can perform similar to 18650. Depending on the flashlight, it might be possible to use 16340 (Li-Ion RCR123A) or 17650 (Li-Ion) batteries, which are rechargable.

In general, it is cheaper to use rechargable batteries since one Ni-MH can replace 500-1000 Alkaline/Lithium and one Li-Ion can replace 300-1000 Lithium. If those 500 Alkaline were purchased at $0.10 each, that is still $50 in batteries replaced by one battery for under $5. If the Lithium version could be purchased at $1.00 each, those 500 would be $500, again covered by a single Ni-MH for under $5. As for the Li-Ion, one $25 18650 battery getting 300 charge cycles would have be replaced by 300 pairs of CR123A Lithium - 600 batteries total - and even at $1.00 each that is $600 in batteries.

Spending $80 on 8 AA Ni-MH and a fancy charger would replace at least [500*8] 2000 (over $200) of AA Alkaline or Lithium batteries. When the Ni-MH do eventually fail, $30 gets another 8 Ni-MH and replaces at least another 2000 Akaline/Lithium batteries.

Spending $100 on a pair of 18650 and a fancy charger would replace at least [300*2*2] 1200 (over $1200) CR123A Lithium batteries. Then the 18650 do eventually fail, another $50 gets another pair of 18650 and replaces at least another 1200 CR123A batteries.

If you want to know more, below is enough information to get started or just make an informed decision.


Voltage

Batteries supply different voltages at different discharge rates. This is impacted by chemisty and charge level of the battery. For this reason, batteries are given a nominal voltage rating that is derived in some fashion to indicate the voltage output the battery will typically be supplying. All you really need to know is that batteries are given a voltage rating and devices request batteries by that rating.

Common voltage ratings of batteries are as follows:

1.5V - Alkaline, Lithium

1.2V - Ni-MH

3.7V - Li-Ion, LiFePO4

Capacity (mAh)

Batteries can only hold a limited amount of electricity. How much a battery can hold is influenced by chemistry and physical size. A bigger battery can hold more, but also takes up more space.

mAh is milliamperes per hour - which can also be represented by Ah (amperes per hour) and can be converted by dividing the mAh by 1000 (3400mAh = 3.4Ah). This value represent how many amperes can be supplied in an hour at a certain discharge rate. A company may indicate what discharge current (C) or the discharge time of the battery. If neither is given, it is pressumed to be discharged over 8 hours.

What is important to note is that mAh is only useful when comparing the same size battery (AAA, AA, C, D, 9V, 18650, 17650, 10440, 14500, 16340, etc) that are the same chemistry (alkaline, lithium, Ni-MH, Li-Ion).

When comparing mAh between brands of batteries, there will likely be some variation at the same capacity. One brand's 3400mAh battery might last slightly longer while the other brand's 3400mAh battery handles slightly higher demands - such as a slightly brighter flashlight.

When it comes down to it, real world use will be different from the factory testing that gives the ratings. So, keep it simple - high mAh means higher runtimes... and don't mix batteries of different mAh, voltage, brand or chemisty.

Chemistry

There are plenty of chemistries for batteries. The chemistry changes attributes of a battery: voltage, capacity, use cycles.

We stock batteries with a chemistry suitable to the flashlights we sell: Alkaline, Lithium, Ni-MH, Li-Ion, LiFePO4.

Even among particular chemistries, batteries can be built differently. This means mixing batteries from different brands can be harmful to the batteries, the device they are in or anything in their vicinity. Each brand builds batteries according to their preferences but even with the variations there are some constants that are maintained.

- Alkaline Primary

Voltage Rating: 1.5V

Capacity (mAh): Highest rating, lowest practical.

Recharge Cycles: None (do not attempt to recharge)

Pricing: Cheapest due to current mass production.

Recyclable: Yes, low value.

Self Discharge: Yes - hazardous when fully depleted.

Hazards: Alkaline batteries eventually leak - not if the leak, when they leak - the chemicals that leak from the battery will corode materials they come in contact with. This often leads to the damage to the device they are in. Leakage occurs when the battery is depeleted beyond usable levels - since batteries self drain in storage, thise state will eventually be achieved. In low or high temperature environments, Alkaline will self-drain faster... in environments that fluctuate between high and low temperatures they drain even faster. If the temprature gets too high (fire, oven, mircowave) then the battery may explode and launch shrapnel. Shorting (directly connecting the two ends of the battery) can result in high enough temperatures to start a fire before the battery has discharged.

Notes: Alkaline batteries are the most abundant and most used in households. While they have a high rating for capacity, they don't use their full capacity in high demand electronics. While they are recyclable it is not particularly worth it financially but it is worth it for sustainability and the environment, most people discard them. These are also the most destructive to the environment.

- Lithium Primary

Voltage Rating: 1.5V / 3.0V

Capacity (mAh): Similar to Alkaline, slightly less or slightly more.

Recharge Cycles: None (do not attempt to recharge)

Pricing: Two to four times the price of Alkaline.

Recyclable: Yes, good value.

Self Discharge: Yes

Hazards: If the temperature gets too high (fire, oven, microwave) then the battery may explode and launch shrapnel. Shorting (directly connecting the two ends of the battery) can result in high enough temperatures to start a fire before the battery has discharged - the higher voltage versions are more likely to acheive fire starting temperatures before discharging.

Notes: Lithium batteries are becoming decently available. Supplies more capacity in high demand devices, thus lasting longer than Alkaline even when the rated capacity is lower than the same size Alkaline battery. Easily recycled into batteries again and financially worth it for companies that perform the recycling.

- Ni-MH Rechargable

Voltage Rating: 1.2V

Capacity (mAh): Slightly less than Alkaline / Lithium.

Recharge Cycles: 500-1000

Pricing: Similar to Lithium, in addition a charger is required.

Recyclable: Yes, reasonable value.

Self Discharge: Yes - some versions of Ni-MH have reduced self discharge rates.

Hazards: If the temperature gets too high (fire, oven, microwave) then the battery may explode and launch shrapnel. Shorting (directly connecting the two ends of the battery) can result in high enough temperatures to start a fire before the battery has discharged.

Notes: With a lower voltage rating, Ni-MH batteries aren't effective in all high demand devices - but many devices can handle the slightly less voltage and will get more capacity from the Ni-MH over an Alkaline. In low demand devices, Ni-MH perform similar to Alkaline batteries. Recycling is reasonable and financially worth if for companies that perform the recycling.

The main advantage of Ni-MH over Alkaline and Lithium is the rechargablility. One Ni-MH battery can be typically recharged 500-1000 times. Taking into account the initial cost of setup (Ni-MH usually come in packs of four and a charger is needed), they are cheaper than sticking to primary batteries.

Price out these three scenarios to see the cost difference:

1) Ni-MH Charger (I recommend pricing with the most expensive charger we carry or you can find), 4pk AA Ni-MH, 4Pk AAA Ni-MH [each battery can be recharged at least 500 times, making that a minimum of 2000 AA racharges and 2000 AAA recharges].

2) 2000 AA Alkaline, 2000 AAA Alkaline

3) 2000 AA Lithium, 2000 AAA Lithium

- Li-Ion Rechargable

Voltage Rating: 3.7V / 3.0V

Capacity (mAh): Less than half of Alkaline / Lithium capacities.

Recharge Cycles: 300-500-1000

Pricing: Around double the price of Lithium.

Recyclable: Yes, good value.

Self Discharge: Yes

Hazards: If the temperature gets too high (fire, oven, microwave) then the battery may explode and launch shrapnel. Shorting (directly connecting the two ends of the battery) can result in high enough temperatures to start a fire before the battery has discharged - versions with protection circuits will prevent this from occuring. If the battery temperature gets too high then a built in valve will trigger and release some of the battery contents, which will destroy the battery - versions with protection circuits will attempt to prevent this from occuring (external heating such as fire, oven, micrwave, etc. cannot be solved by a protection circuit).

Notes: Li-Ion batteries have a much higher voltage rating so they can't be used in devices that aren't designed for Li-Ion batteries. While they have much less capacity, they supply their capacity as well as a Lithium primary battery. They are easily recylced back into batteries and are financially worth it for companies recycling batteries.

When it comes to high demand devices, those designed to use Li-Ion perform better than the same device designed to run on Alkaline/Lithium/Ni-MH. This is because of the higher voltage capabilities in the Li-Ion chemistry. By reducing the rate that power is drawn from the battery, the effective capacity of a Li-Ion battery can be extended.

At this point Li-Ion batteries may sound like they aren't worth it, however a comparison of some flashlights we carry shows otherwise:

Armytek Prime A2 - 2*AA, max 500 lumens (OTF) for 1 hour.

Armytek Prime C2 - 1*18650, max 1050 lumens (OTF) for 1 hour and 30 minutes.

Eagletac SX25A6 - 6*AA, max 932 lumens (FL1) for 1 hour and 48 minutes.

Eagletac GX25A3 - 3*AA, max 832 lumens (FL1) for 1 hour and 18 minutes.

Eagletac G25C2 MkII - 1*18650, max 980 lumens (FL1) for 1 hour.

Eagletac GX25L2 NR - 2*18650, max 878 lumens (FL1) for 2 hours.

Fenix E41 - 4*AA, max 400 lumens (FL1) for 2 hours and 30 minutes.

Fenix TK09 - 1*18650, max 450 lumens for 2 hours.

The Armytek flashlights show the best comparison since they are the same flashlight just designed slightly differently to handle the difference in voltage. The other flashlights demonstrate how many batteries are needed to make lights that compete with those designed for Li-Ion batteries.

- LiFePO4 Rechargable

Voltage Rating: 3.2V / 3.0V

Capacity (mAh): Similar to regular Li-Ion

Recharge Cycles: 300-500-1000

Pricing: Similar to Li-Ion

Recyclable: Yes, good value.

Self Discharge: Yes

Hazards: If the temperature gets too high (fire, oven, microwave) then the battery may explode and launch shrapnel. Shorting (directly connecting the two ends of the battery) can result in high enough temperatures to start a fire before the battery has discharged - versions with protection circuits will prevent this from occuring. If the battery temperature gets too high then a built in valve will trigger and release some of the battery contents, which will destroy the battery - versions with protection circuits will attempt to prevent this from occuring (external heating such as fire, oven, micrwave, etc. cannot be solved by a protection circuit).

Notes: This is another Li-Ion chemistry but the slight drop in voltage is worth taking note. Aside from the slightly lowever voltage, these are pretty much the same as Li-Ion chemistry batteries.

Battery Sizes

Batteries are available in more sizes than most people know about... but many of those sizes most people don't need to know about. Below is mainly the sizes we carry, though some we carry will not be included and some we don't carry might be included.

AAA

A battery size common in households as many home devices use this size. AAA batteries are around 44.5mm long and 10.5mm in diameter. These are rated 1.2V or 1.5V, depending on the chemistry of the battery.

10440

Li-Ion version of the AAA, these are around 44.0mm long and 10.0mm in diameter - hence 10440. These are rated 3.7V and should never be used to replace AAA batteries unless the device is designed for Li-Ion batteries.

10460

Commonly refered to as a Protected 10440 or just 10440, these batteries measure 46.0mm long and 10.0mm in diameter. These are a 10440 battery with a protection circuit installed to prevent overcharging, over discharging, overheating, shorting and possibly more. These are still rated 3.7V and should only be used in devices designed to use Li-Ion batteries.

AA

The most common battery size in households as more devices use AA over AAA. They measure around 50.5mm in length and 14.5mm in diameter. These are rated 1.2V or 1.5V, depending on the chemistry of the battery.

14500

Li-Ion version of the AA, they measure around 50.0mm long and 14.0mm in diameter - hence 14500. These are rated 3.7V and should never be used to replace AA batteries unless the device is designed for Li-Ion batteries.

14510

Commonly refered to as a Protected 14500 or just 14500, these batteries measure 51.0mm long and 14.0mm in diameter. These are a 14500 battery with a protection circuit installed to prevent overcharging, over discharging, overheating, shorting and possibly more. These are still rated 3.7V and should only be used in devices designed to use Li-Ion batteries.

C

This used to be a common battery size - mostly for flashlights. They measure 50.0mm long and 26.2mm in diameter. These are rated 1.2V or 1.5V, depending on the chemistry of the battery.

D

This used to be a common battery size - mostly for flashlights. They measure 61.5mm long and 34.2mm in diameter. These are rated 1.2V or 1.5V, depending on the chemistry of the battery.

9V

Named for their voltage output, these are another common household battery as some home devices use them. No matter what chemistry, these batteries are designed to a rating of 9V. These measure roughly 48.5mm long, 26.5mm wide and 17.5mm thick and are a rectangular cube shape. These are the only size of battery that chemistry does not typically restrict usage. These are also the battry size to have the most problems due to shorting because both connection points are beside eat other - care should be taken when storing 9V batteries so no conductive materials or other batteries can come into contact with the connection points.

CR123A

Also refered to as a camera battery due to their primary use having been in cameras. These measure 34.5mm long and 17.0mm in diameter and are almost exclusively Lithium chemistry. CR123A batteries are most commonly have a 3.0V rating.

16340 (RCR123A)

Li-Ion version of the CR123A, these are also commonly refered to as RCR123A. These are around 34.0-34.5mm long and can be 16.0-17.0mm in diameter. While most are rated 3.7V, there are some designed to be 3.0V to match the CR123A batteries. Only the 3.0V versions can be used to replace CR123A batteries unles the device is designed to handle 3.7V Li-Ion batteries.

Protected 16340 batteries are typically 34.5mm long and 17.0mm in diameter, but they can be smaller. Due to this fluctuation in sizing, 16340 covers both protected and unprotected versions.

17670

These Li-Ion batteries measure around 67.0mm long nd 17.0mm in diameter. These are a protected 17650 battery. These are almost the length of two CR123A batteries, making it a viable replacement for a pair of CR123A batteries. However, the lower voltage of a single Li-Ion (3.7V) compared to a pair of Lithium (3.0V * 2 = 6.0V) can result in lower outputs; the trade off is the use of a rechargable battery that can replace over 600 CR123A batteries.

18650

These Li-Ion batteries measure around 65.2mm long and 18.6mm in diameter with a 3.7V rating. 18650 is typically used in reference to the protected versions as well.

18670 / 18690

These are 18650 batteries with protection circuits added and they measure 67.0-69.0mm in length and 18.0-19.0mm in diameter. Often times, these batteries are refered to as Protected 18650 or just 18650. This battery is becoming the battery of choice for flashlights.

Batteries in Series vs Parallel

When using multiple batteries in any device, they can be connected in series or in parallel. Each has advantages and disadvantages. When placing batteries in series or parallel, all batteries must be the same voltage and capacity (mAh) or the higher voltage/capacity batteries will result in damage to the lower voltage/capacity batteries.

Series:

Batteries in series are effectively in a row (either physically or electrically) - this is the more commonly used system. The most basic is a two battery physical series where one battery is loaded in so one end connects to the device's elecronics, then the second battery is loaded facing the same direction so it make contact with the other battery and the other connection to the device's electronics. A more complex example of batteries in series is a battery cradle where one battery is loaded facing one direction, the next facing the opposite in the next section and another facing the same as the first - the batteries aren't physically connected to each other, but wires in the cradle connect the ends of the batteries so they are in series and in this example the devices connection of the cradle would be on the same end for loading.

Advantages: The voltage of each battery in the series is added to the others. Four Alkaline batteries would be (1.5V * 4 = ) 6.0V. Four Ni-MH batteries would be (1.2V * 4 = ) 4.8V. Four Li-Ion batteries would be (3.7V * 4 = ) 14.8V.

With the the increased voltage, flashlight output is increased. This makes three Ni-MH batteries (1.2V * 3 = 3.6V) competetive in output with a single Li-Ion battery (3.7V). A pair of Alkaline or Lithium batteries (1.5V * 2 = 3.0V) are also reasonable competition.

Disadvantages: The capacity does not increase. With three 1000mAh batteries in series, the total capacity of the 'battery pack' is still only 1000mAh. With a voltage regulating circuit that limits the voltage coming from the batteries, the capacity is drained slower.

As batteries deplete the voltage they put out drops resulting in a drop of performance. If one battery has less charge than the others (for example, of three batteries one is nearly depleted and the other two are near full) then the total then the total voltage will drop and result in being below the device's required voltage before the higher charged batteries have fully discharged. With Alkaline or Lithium, this can result in batteries being discared before they are fully drained - and the if the Alkaline is over discharged then it could begin leaking at any time. With Ni-Mh or Li-Ion, this gives the appearance that capacity has decreased when it hasn't - it can also result in the under charged battery being over discharged which disables the battery to it can not longer be charged (Li-Ion protection circuits prevent this from occuring).

In the case where one battery has a higher charge, the same results as above will occur, but sooner since the voltage will be lower to begin with. For example, three batteries with one nearly full and two only half full. When the two half full are depleted, the deviec will no longer recieve enough power and the result is the fuller charged battery no long is drained. If the difference between the full battery and the drained batteries is great enough, the drained batteries may be over discharged before the voltage gets too low for the device.

Shorting:

In the case of a circuit short, the temperature of the batteries will rise quickly and higher than a single battery would but last as long as a single battery would. This can result in batteries leaking, burning anything they make contact with or potentially igniting flamable materials. (Li-Ion protection circuits prevent this by disconnecting the battery from the circuit.)

In the case of a battery short (the battery fails and self drains quickly) it will heat up and potentially damage the other batteries, cause burns, leak or start a fire.

Parallel:

Batteries in parallel instead increase the total capacity of the 'battery pack'. This is where battteries are electrically connected on the same ends. When batteries are loaded into a device facing the same direction or in a cradle facing the same direction then they are likely in parallel.

Advantages: In a device that can run just as well on a single battery as on a pack of those batteries in parallel, the capacity (runtime) is effectively multiplied by the number of batteries. With three 1000mAh batteries, the effective capacity is 3000mAh.

Some devices require drawing the power quicker than a single battery can support; drawing even slightly faster than the battery is rated for can significantly impact the drain rate of the battery and result in greatly lowered runtimes. With a pack of batteries in parallel, the demand is spread among the batteries which allows for the regular rate of capacity drain and runtime.

Disadvantages: If one battery fails then the effective capacity drops respectively.

If the batteries are not close to equally charged then those with lower charge are highly likely to be over discharged. In Alkaline batteries, this results in leaks. In Ni-Mh and Li-Ion this will disable the battery so it cannot be recharged (Li-Ion protection circuits prevent over discharge).

Shorting:

In the case of a circuit short, the temperature of the batteries will rise quickly and could last longer than a single battery would. This can results in batteries leaking, burning anything they make contact with or potentially igniting flamable materials. (Li-Ion protection circuits prevent this by disconnecting the battery from the circuit.)

In the case of a battery short (the battery fails and self drains quickly) it will also behave as a circuit short for the other batteries in the pack; all the batteries will heat up and potentially cause burns, leak or start a fire. (Li-Ion protection circuits will prevent other batteries in the pack from being drained by the failing battery but they may still be damaged by the heat generated by the failing battery.)

Series and Parallel:

This is achieved by placing batteries in series and then placing those groups of batteries in parallel to each other. Each seperate pack of batteries in series would have to have equal number of batteries so they are the same voltage when placed in series.

An example setup would be nine batteries divided into groups of three. The three batteries in each group is connected to each other in series and then each group is connected to each other in parallel. The voltage would be determined by the batteries in series (each group of three) and the capacity would be based on the packs being in parallel (three groups).

With nine Ni-MH 1.2V 1000mAh batteries each group in series would be (1.2V * 3 = )3.6V and 1000mAh. Then the three groups in parallel would be (1000mAh * 3 = ) 3000mAh at 3.6V. This would be a battery pack that is rated 3.6V with a capacity of 3000mAh. [Note: This is about the same as a single Li-Ion 18650 battery at 3.7V and 2800-3400mAh.]

Advantages: The voltage increase of batteries in series and the capacity increase of batteries in parallel.

Disdvantags: All the disadvantages of series and parallel. More batteries to be damaged by one battery having more or less charge, which is why battery packs are typically made to be charged as a group instead of each battery individually.

Shorting:

In the case of a circuit short, the higher voltage and capacity greatly increases the hazards from such a short. Battery packs should have a protection circuit to disconnect from the device if a circuit short does occur.

In the case of a battery short (the battery fails and self drains quickly) it will heat up and potentially damage the other batteries, cause burns, leak or start a fire. Since each group of three batteries are in series, a single battery self-shorting can damage the batteries around it through heat or leaking. If the pack of batteries in series containing the failed battery is still used after the battery has failed it will have a reduced voltag reduce the device's performance.

Series vs Parallel Summary:

Higher voltage or capacity demands can be met by adding more batteries in series or parallel as needed... but each battery added increases the potential complications and hazards should something fail. Care should be taken to prevent circuit shorting from occuring and avoid over charging or discharging of batteries.

Series and Parallel in Flashlights We Carry:

Most (if not all) the flashlights we carry that require multiple batteries run those batteries in series - either physically (in a row) or electrically (battery cradle or body wiring) to get increased voltage for output and may include a votage regulator to limit the extra voltage drawn to extend runtime. Some have optional expansion to add more batteries in series (Eagletac 3-cell Body Extension or Eagletac 4-cell Body Extension) and the flashlight has a built in voltage regulator so it only draws as much voltage as it requires and results in an effectively increased runtime.

The Fenix LD50 is neither series nor parallel but does simulate batteries in series. One battery compartment powers one LED while the other battery compartment powers the other LED. Instead of using series batteries to increase voltage to get more output from the LED, two LEDs are used to generate more output. This results in the same runtime as one LED powered by two batteries in series. The advantage is the option to only use one battery compartment for reduced output at the same runtime.

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Battery Chart

Below are the various battery sizes we carry for use with our products, there are plenty more available (and we can likely get them), but our selection is based on the products we sell. We do carry some outside what our products use. Numbered batteries, such as 10440, are given a number based on their dimensions. 10mm by 44mm makes it a 10440. Protected versions of batteries commonly just add a protection circuit that is usuually 2-3mm thick, adding that much to the height. For that reason, they are technically a different battery, but commonly are just referred to by the battery that has the protection: 10460 is commonly known as protected 10440.

Battery

 Alternate Name

Dimensions (mm) (diameter x length) (h * w * l)Example Capacity** (mAh)Comments
         
AAA - 10.5 * 44.5 alkaline - 1200mAh NiMH - 1000mAh lithium - 1100mAh  
AA - 14.5 * 50.5 alkaline - 2700mAh NiMH - 2500mAh lithium - 2900mAh  
C - 26.2 * 50.0 alkaline - 8000mAh NiMH - 5000mAh  
D - 34.2 * 61.5 alkaline - 12,000mAh NiMH - 10,000mAh  
9V - 48.5 * 26.5 * 17.5

alkaline - 565mAh NiMH - 200mAh lithium - 600mAh li-ion - 500mAh

Somtimes refered to as a 1604, might include a letter to indicate the chemistry.
CR123A - 17.0 * 34.5 lithium - 1700mAh Some versions are actually slightly smaller in dimensions.
10440 - 10.0 * 44.0 li-ion - 300mAh AAA Size***
10460 Protected 10440 10.0 * 46.0 li-ion - 300mAh Protected version of a 10440. May be refered to as a protected 10440.
14500 - 14.0 * 50.0 li-ion - 750mAh AA size***
14510 Protected 14500 14.0 * 51.0 li-ion - 750mAh Protected version of a 14500. May be refered to as a protected 14500.
RCR123A 16340 17340

Rechargable CR123A

16.0 * 34.0 17.0 * 34.5 li-ion - 750mAh Li-ion (rechargable) version of the CR123A. These are usually the protected version. There isn't really a set standard for this battery, so long as it is 'close' in size. Since CR123A is sized 17345, either size will work.***
17650 17670 - 17.0 * 67.0 li-ion - 1600mAh This is almost double the length of a CR123A.
18650 - 18.6 * 65.2 li-ion - 3400mAh This is an unprotected li-ion battery.
19670 19690 18650 19.0 * 67.0 19.0 * 69.0 li-ion - 3400mAh Protected version of the 18650. Actuall size varies between the two sets of dimensions. Commonly, these are listed in sales as 18650 but it is also as common for products that ask for 18650 to be refering to protected version. These are the variety we use and sell.
**Capacity is only useful for comparing to batteries of the same size and chemistry. Capacity testing methods can differ slightly between companies, so one 3400mAh may be slightly better than another 3400mAh.
***Li-ion versions of batteries are higher voltage. Only use Li-ion batteries in devices that are designed to handle them.

 

For more information about batteries, there is a wikipedia article.

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