18650 Battery vs 2x CR123A Batteries vs 3x AAA Batteries
At first, 18650, CR123A and AAA batteries are very different cylindrical batteries - they differ in physical dimensions, chemistries, nominal voltages, capacities, discharge characteristics and also have other features that differ significantly.
Nonetheless, having a device that supports two or more battery types allows the user to choose the best battery (or batteries) according to the intended use of the device or, in emergencies, allows the user greater freedom in finding at least "some" kind of battery in order to power the device.
Published: October 30, 2021.
Features and Specifications of 18650, CR123A, and AAA Batteries
Physical dimensions of the 18650 battery are (D x H) 18 × 65 mm (0.70866 x 2.5590 inches), while nominal voltage and capacity depend on the actual battery chemistry and the type and vary between 3.2 and 3.7 volts and generally between 3000-6000 mAh (3-6 Ah).
18650 battery is a rechargeable battery with some models intended as high-capacity low-drain batteries or as high drain, low-capacity batteries.
When they are not in use, it is recommended to recharge them every 3-6 months.
For more information about these batteries, feel free to check our How to Pick the Best 18650 Battery and 18650 Battery Charger article.
Physical dimensions of the CR123A battery are (D x H) 17 x 34.5 mm, with a nominal voltage of 3.0V and nominal capacity of ~1500 mAh (~1.5 Ah).
CR123A battery is a non-rechargeable battery, with a shelf life often of 10+ years. CR123A batteries are known for their ability to provide strong currents even after a long time of not being in use.
Some brands also offer rechargeable CR123A batteries often labeled as RCR123A with a nominal voltage between 3.2 and 3.7 volts and a capacity of 500-800 mAh.
For more information about these batteries, feel free to check our Best CR123A Battery - Rechargeable vs Non-Rechargeable Lithium CR123A Batteries article.
AAA batteries are cylindrical batteries with physical dimensions of (D x H) 10.5 x 44.5 mm, while nominal voltage and capacity depend on the exact battery chemistry, as given in the following comparison chart:
Note: when somebody refers to "AAA battery", generally one refers to the non-rechargeable 1.5V AAA battery based on the zinc-carbon or more commonly alkaline chemistry.
Each of these chemistries has its own pros and cons - for more about these batteries, feel free to check our AAA Batteries - Size, Chemistry Types, and Replacements article.
When comparing 18650, CR123A, and AAA batteries, it is very important to start with their physical dimensions:
- 18650 battery: 18 x 65 mm,
- CR123A battery: 17 x 34.5 mm,
- AAA battery: 10.5 x 44.5 mm.
As one can see, when two CR123A batteries are placed one on another, one gets a battery pack with physical dimensions of ~17 x 69 mm.
Also, when three AAA batteries are placed next to each other, they fit the cylinder that features a diameter of ~22 mm which is 44.5 mm high.
- 18650 battery: 18 x 65 mm,
- 2x CR123A batteries: 17 x 69 mm,
- 3x AAA batteries: ~22 x 44.5 mm.
Now, the dimensions are not that different!
Some brands offer their devices, mostly LED flashlights, but there are other devices as well, with special battery adapters/holders that allow these three batteries to fit the same battery compartment, allowing the user to power the device with the most suitable battery/batteries.
Note: most devices powered by a single 18650 battery may accept two CR123A batteries easily (if the battery compartment is long enough) without any battery adapter/holder. However, this should NOT be done unless the device's manufacturer explicitly allows - higher voltage of 2x CR123A batteries may easily damage/destroy devices intended ONLY for 3.2-3.7V of a single 18650 battery.
Stored Energy Comparison
Another important comparison of these three battery options is stored energy comparison:
- 18650 battery: 3.2-3.7V, 3-6Ah → 9.6-22.2 Wh,
- 2x CR123A batteries: 6.0V, 1.5A → 9 Wh,
- 2x RCR123A batteries: 6.4-7.4V, 0.5-0.8Ah → 3.2-5.9 Wh,
- 3x alkaline AAA batteries: 4.5V, 0.85-1.2Ah → 3.8-5.4 Wh,
- 3x NiMH AAA batteries: 3.6V, 0.6-1.3Ah → 2.1-4.7 Wh,
- 3x Li-ion AAA batteries: 10.8-11.1V, 0.35-0.6Ah → 3.8-6.7 Wh,
- 3x Li-FeS2 AAA batteries: 4.5V, 1.1-1.3Ah → 4.9-5.9 Wh.
Since modern devices feature highly efficient DC/DC converters, comparison of stored energy is perhaps the most important one.
As one can see, a single 18650 battery is able to store the most energy, when compared with 2x CR123A and 3x AAA batteries.
Personally, if You have a device that supports the use of either single 18650 or two CR123A batteries, for the device that is used often, go for a 18650 battery, and for the device that is used only occasionally (or act as standby/backup device) go for CR123A batteries with long shelf life.
A similar recommendation goes for devices that support the use of a single 18650 battery, or two CR123AA batteries or three AAA batteries - use AAA batteries only when required 18650 or CR123A batteries are not available.