21700 vs 18650: What is the Difference & Which One is Better?

Susan Fernandez November 11 2021

Lithium-ion batteries offer numerous advantages to the users and no wonder they are widely used in the new energy vehicle field. The lithium-ion batteries were first introduced by Sony and were the best because of their safety and high energy density. 

A number of people have a raging debate about 21700 vs 18650 and their pros and cons, as both of these are widely used cylindrical lithium-ion batteries. It is never easy to compare both because both are developed as high-performance battery packs for vehicles, appliances, and cutting-edge tools.

What is a 21700 battery?

These are rechargeable lithium-ion cells that follow a nomenclature based on their diameter and length. The high density of the 21700 makes them a good choice for battery packs of higher capacity. On the other hand, a new 21700 lithium-ion battery can be charged quickly and doesn’t require any prolonged charging.

21700 is used in electric bikes, flashlights, cars, different types of power tools, and electric wheelchairs. Although the 21700 lithium-ion battery offers a higher capacity output, it is expensive to manufacture. 

The technology giants Panasonic and Samsung SDI had earlier launched an upgraded version of the cylindrical lithium-ion battery which is known as the 21700 battery. Few companies had already started manufacturing them while most were still using the 18650 type.

As for 21700 battery, they are considered the best batteries for high-drain electronic cigarettes. Furthermore, they can also power e-cigs with low resistance atomizers without any problems. But you have to make sure that your device is compatible with it before choosing this type of battery.

Characteristic

Most importantly, safety measures are now being observed in these batteries because of the dangers involved in using them. They are made with LiNiCoMnP cathodes which are safer compared to their predecessors with minimal risks of short-circuiting or catching fire if charges improperly. They still come at a higher price but we can't really compare them because 18650 batteries were first introduced and had been already used long ago by companies and shops everywhere.

As for their applications, 21700 batteries are primarily used in electric cars and power tools. Furthermore, they can also be used as a replacement battery for a laptop or a cordless drill. These batteries come with several advantages over the 18650 type but it still pales when compared to other types of cylindrical lithium-ion batteries. For instance, they have longer cycle life along with higher energy density which means that you'll be getting less charge time than what you get with 18650 cells.

There's no question about these two types of batteries because both are excellent in terms of performance and capacity. But if you want superior safety measures to protect your precious homes and loved ones from fires caused by faulty devices, then investing in the latest 21700 battery is an excellent choice.

However, some manufacturers use 18650 batteries to power their devices because of their compatibility with most e-cig brands. It's still best to choose the latest 21700 battery if you want more power for vaping and longer run time per charge which can actually save you a lot of money in the long run.

A list of pros & cons for 21700 battery types based on research findings from various sources

Pros:

  • Heavier and more rugged than their small counterparts, 20700 batteries are very similar in size to 18650 cells
  • More capacity per volume or mass compared to other cylindrical battery types (80+ Wh/kg)

 Cons:

  • Heavier and slightly larger than other 18650 batteries of similar capacity.
  • Costlier than other 18650 cells due to lower manufacturing volume/complexity
  • Generally less power per unit volume or mass vs. competing battery types: 20700, 21700, etc.

What is a 18650 battery?

This is also a rechargeable lithium-ion battery that has a diameter of 18mm and a length of 65mm. This battery is smaller as compared to the 21700 but is highly efficient, and therefore, it has a good balance between the energy produced and the discharge rate. 

Among all the batteries in the market, 18650 has the largest market share, and this has made its manufacturing economical.

Characteristic

One of the most notable features of a 18650 battery is that it has a lot to offer regardless if you are vaping, using flashlights, or even building an electric car. They are made with LiCoO2 cathode which has cobalt components in its structure for enhanced performance. It can be said that they are actually rechargeable lithium-ion batteries meant for high-end appliances and tools.

If you want to get more power out of these cells, then it's essential to have the latest technology in the market because there are serious chances that your current battery will catch fire at any time. Also, their production cost varies from manufacturer to manufacturer, so choose wisely when you buy them.

As for their applications, these batteries are being used in laptops, medical devices including ambulances, and electric vehicles. Their main disadvantages are that they have a higher self-discharge rate compared to other types of batteries. But nowadays, many experts are coming up with new breakthroughs to address some of the issues with the 18650 batteries.

Over the years, there has been a constant enhancement in the efficiency and capacity of 18650, and it is also generally safe. 18650 batteries are primarily used in electronic devices, flashlights, laptops, and a few electric cars. 

A list of pros & cons for 18650 battery types based on research findings from various sources

Pros:

  • Longer lifespan (500-700 charge cycles)
  • Heavier and more rugged than their small counterparts
  • Higher maximum discharge current compared to other cylindrical battery types (20A+)

Cons:

  • Costlier than other 20700 cells due to lower manufacturing volume/complexity
  • Generally less power per unit volume or mass vs. competing battery types: 18650, 21700, etc.
  • Some sources indicate that the first generation of protected 18650 batteries has some reliability issues with some brands/models of protected cells having a risk of the protection circuit activating even with minimal cell stress during charging causing overcharging and possible safety hazards.

Differences between 21700 vs 18650 lithium-ion batteries

Size

Size is among the most apparent differences between 21700 and 18650 batteries, and whether this can be a factor to choose them for the applications is something that one can take up separately.

Capacity

There is always a higher capacity for the bigger size, and this is also the general rule for lithium-ion batteries. Although it may not be that difficult to understand, it is worth noting that the larger batteries require more charging time.

Energy

When you have more energy, it means more runtime for a battery. When comparing 21700 vs 18650, the mAH of 18650 is in the range of 2000 to 3500. On the other hand, 21700 batteries have a range of 3000 to 5000 mAH. 

Gravimetric energy density

This unit is used to measure the weight efficiency of any battery. The gravimetric energy density of 21700 is in the 218 Wh/kg range, while 18650 has around 223 Wh/kg range. Therefore, there may not be much to choose between both the batteries in terms of weight efficiency.

Final Points

In terms of output and efficiency, there may not be much to choose between the 21700 vs 18650 lithium-ion batteries. The quality of both these batteries depends on the credentials of the manufacturer and the brand. Therefore, it is crucial to consider the safety factors before you select a particular battery pack for your device. With proper care and maintenance, 21700 vs 18650 batteries are worth the investment.