Battery Equivalents and Replacements

18650 Battery vs. AA Battery

Both 18650 and AA batteries are cylindrical batteries that differ in size, and that come in various types of battery chemistries, thus differing in the battery voltage, capacity, and other charging/discharging characteristics.

In order to simplify finding the batteries for their devices, some manufacturers ship their 18650 devices (mostly flashlights) with an AA battery holder that allows AA batteries to be used in the 18650 battery compartments. But is this actually a good idea?

Updated: November 4, 2022.

protected 18650 battery

18650 and AA Batteries Features and Specifications

18650 batteries are rechargeable lithium-ion batteries featuring physical dimensions of 18 × 65 mm (0.70866 x 2.5590 inches), a nominal voltage between 3.2 and 3.7 volts, and a nominal capacity between 1800 and 5000 mAh.

Since lithium-ion batteries are relatively sensitive to charging and discharging conditions, some 18650 batteries feature a small Battery Management System (BMS) that protects the battery from unwanted events - such 18650 batteries are called "protected 18650" batteries.

Also, 18650 batteries differ in the form of the positive terminal - there are "flat top" batteries and "button-top" batteries.

Which type suits your needs, You have to find it by reading the manual of the device you have.

Since lithium chemistries don't suffer from the memory effect, 18650 batteries may be recharged as soon as one can put them in the charger, assuming that they are not too warm or too cold.

The most popular 18650 battery brands are Panasonic, Samsung, LG, Sony, Molicel, Epoch, and similar.

aa battery 3

AA batteries feature physical dimensions of 14.5 x 50.5 mm (~0.571 x 1.988 inches) and are available in numerous chemistries, as shown in the following comparison chart:

Chemistry Common Name Rechargeable Typical Capacity (mAh) Voltage (V)
Zinc Carbon R6, 15D No 600 - 1600 1.5
Alkaline LR6, 15A No (Mostly No) 1800 - 2700 1.5
Li-FeS2 FR6, 15LF No 2700 - 3300 1.5 (1.8 max)
Li-ion 14500 Yes 600 - 2000+ 3.6 - 3.7
LiFePO4 IFR14500 Yes 500-750 3.2
Li-SOCl2 (14505) No 2400-2700 3.5-3.6
Li-MnO2 CR AA No ~2000 3.0
Lithium - Yes 1000-2000+ 1.5
NiCd KR6, 1.2K2 Yes 600 - 1200 1.2
NiMH HR6, 1.2H2 Yes 700 - 2800 1.2
NiOOH - No 2200 - 2700 1.5 (1.7 max)
NiZn ZR6 Yes 1500 - 1800 1.6 - 1.65

"Standard" AA battery is a non-rechargeable alkaline AA battery featuring a nominal voltage of 1.5V and a typical capacity of 1800-2700 mAh.

Note: one of the oldest AA battery chemistries is Zinc-Carbon chemistry with a nominal voltage of 1.5V and a typical capacity of 600-1600 mAh. But, since they feature a relatively high self-discharge rate and are prone to leakages, they are mostly replaced by alkaline AA batteries, although they are still available on the market.

Because of differences in size and chemistry, 18650 and AA batteries are able to store different amounts of energy:

  • High-drain 18650 battery, 3.7V 2000 mAh: 7.4 Wh,
  • Low-drain 18650 battery, 3.7V 4000 mAh: 14.8 Wh,
  • High-capacity, low-drain 18650 battery, 3.7V 5000 mAh: 18.5 Wh,
  • Alkaline AA battery, 1.5V, 1200 mAh: 1.8 Wh,
  • Lithium-ion AA (14500) battery, 3.7V, 1500 mAh: 5.55 Wh,
  • NiOOH (Nickel Oxy-Hydroxide) AA battery, 1.5V 2500 mAh: 3.75 Wh,
  • NiMH (Nickel Metal-Hydride) AA battery, 1.2V 2000 mAh: 2.4 Wh, etc.
  • Li-SOCl2 (Lithium-Thionyl Chloride), 3.6V 2700 mAh: 9.72 Wh

As one can see, the main difference between 18650 and AA batteries is the difference between the amounts of stored energy, with some models of 18650 batteries being able to store 14.8 (or even more) Wh of energy, while the best AA batteries are unable to store more than 5-6 Wh of energy.

Note: Li-SOCl2 (Lithium-Thionyl Chloride) AA batteries are able to store 8-10 Wh of energy and are directly compatible (using a battery adapter) with 18650 batteries due to the very similar voltage, but Lithium-Thionyl Chloride chemistry supports very low discharge currents when compared with 18650 discharge currents.

So, if You are going to replace the single 18650 battery with the battery adapter holding one AA battery, be aware that the output power and the amount of energy are going to be decreased.

Personally, it may be great to have the option to choose between the batteries, but the 18650 battery simply stores much more energy than the AA battery and should be a preferred choice for many devices and gadgets, especially for high-drain devices.

18650 and AA Batteries Frequently Asked Questions (FAQ)

Here are some of the most common Frequently Asked Questions (FAQ) about 18650 and AA batteries:

Can you use AA batteries instead of 18650?

No, generally, a AA battery cannot replace a 18650 battery due to the differences in size, voltage, energy being stored, discharge characteristics, and similar.

However, some devices come with a battery adapter allowing the users to replace one 18650 battery with one AA battery, sacrificing the runtime and often performance.

Is a 18650 battery the same as an AA?

No, these batteries differ in size and hence discharge performance. While 18650 batteries feature various lithium chemistries, AA batteries feature even more chemistries.

But, the main difference is the size and the voltage of the most commonly used 18650 and AA batteries:

  • 18650 battery: 18 × 65 mm (0.70866 x 2.5590 inches), 3.6V
  • AA battery: 14.5 x 50.5 mm (~0.571 x 1.988 inches), 1.5V

What is a 18650 battery equivalent to? Can I use 2 CR123 instead of 18650?

18650 battery is equivalent to a 18650 battery, and that's it.

There are several batteries of similar size, for example, 19670.

But, some devices allow the users to use, for example, two CR123A batteries instead of 18650 without sacrificing the performance.

For more about this topic, feel free to check our 18650 Battery vs. 2x CR123A Batteries vs. 3x AAA Batteries article.

What is so special about the 18650 battery? What battery is bigger than the 18650?

18650 battery is an excellent battery - it is able to store plenty of energy, it features high power output, it is not too large, and it features a relatively large area, which improves cooling.

Thicker batteries, like 26650 and 32650, are able to store even more energy, but when being discharged with really high currents, these batteries will overheat faster than the 18650 batteries.

But, 18650, 26650, 32650, and similar batteries are commonly used in high-drain devices, including laptops, electric vehicles, cordless tools, high-output flashlights, and similar.

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