Today, nearly everything from power tools to telephones to flashlights to laptops to electric vehicles is powered by lithium-ion batteries. They are widely used owing to their rechargeable nature, lightweight, and energy-storing capacity in a confined space. The two most popular types of batteries are 18650 and 21700. These are both cylindrical lithium-ion batteries, though they vary in many aspects, including size, capacity, performance, and applications. It is important to know how they differ so you can select the correct battery for your device, project, or business application.
What Is an 18650 Battery?
An 18650 battery is a cylindrical lithium-ion battery that comes in 18mm x 65mm. These measurements are where the name “18650” originates from. This type of battery has been in use for many years and remains popular in the following applications: Laptop Computers, Flashlights, e-Bikes, Medical Devices, and portable electronics.
There is one huge benefit to the 18650 battery, and that is the fact that they are readily available. Easy to find, typically inexpensive, and compatible with a multitude of devices. The 18650 battery cells come in various sizes and chemistries, with a typical capacity of 2,000 mAh to 3,500 mAh. Usually, it stores less energy than a 21700 battery; however, due to its smaller size. This implies that devices with a 18650 battery may require additional cells to operate for a longer duration.
What Is a 21700 Battery?
The 21700 battery is also a cylindrical Lithium-ion battery, but larger in size than the 18650. It is of a diameter of 21 mm and a length of 70 mm. Due to its larger size, it’s able to contain more active battery material, which may lead to a more powerful capacity and performance.
The battery’s 21700 size is gaining traction in a variety of applications such as electric cars, power tools, energy storage solutions, and high-end devices. They’re especially popular with many manufacturers due to the reduced number of cells required for battery packs of the same capacity. This can help to streamline operations, simplify the pack, and in some cases, even help to reduce pack costs. The 21700 type is particularly beneficial in applications that require extended battery life and high performance.
18650 vs 21700 battery: Main Differences
The most apparent difference between the two battery types is their size, which is 18650 vs 21700. The additional size of the 21700 is what makes it bigger, and it’s that extra power that’s what makes it store more energy. But with bigger doesn’t come better for all circumstances. This will depend on the equipment, space, power consumption, and budget.
| Feature | 18650 Battery | 21700 Battery |
| Size | 18 mm x 65 mm | 21 mm x 70 mm |
| Capacity | Usually 2,000–3,500 mAh | Usually 3,000–5,000 mAh |
| Energy Density | Good | Usually higher |
| Runtime | Shorter compared to 21700 | Longer runtime |
| Power Output | Suitable for many devices | Better for high-drain use |
| Cost | Usually cheaper per cell | Often more expensive per cell |
| Typical Applications | Laptops, flashlights, e-bikes, small electronics | EVs, power tools, energy storage, high-performance devices |
To put it simply, 18650 batteries are inexpensive, dependable, and compact. These are a suitable choice for devices that are already built around this size. The format 18650 has existed for a long time, so there are various brands, models, chargers, holders, and battery management systems for 18650 batteries.
There are 21700 batteries, however, with better performance. They tend to have more capacity and, therefore, last longer between charges. They will also facilitate greater output in the present, which is suitable for applications that require high energy, like electric vehicles and cordless tools. One such advantage is that the number of 21700 cells required to construct a battery pack could be reduced, making the battery pack cleaner and more efficient.
However, it isn’t always best to use 21700 batteries. They are bigger and might not fit into the devices that accommodate 18650 cells. They may also have a higher initial price tag. One of the initial considerations for users replacing batteries in an existing device is physical compatibility.
Which Battery Should You Choose?
If you are looking for a small, cheap, and easily available battery, select a 18650 battery. Great choice for flashlights, laptops, small power banks, do-it-yourself projects, and devices that are already used with this size. Also, it’s more convenient for someone who would like to replace it easily and doesn’t want to spend too much money at first.
If runtime, capacity, and power are what you’re looking for, opt for the 21700 battery. It’s more appropriate for electric vehicles, power tools, e-bikes, solar storage systems, and other purposes that have a high demand. If you have a device or battery pack that has been designed to operate on 21700 cells, it can provide more efficient use, and fewer cells are required.
The choice for DIY should be based on space constraints, voltage needed, battery capacity, and the battery management system (BMS) used. Safety is also of great importance; use quality batteries from reputable manufacturers; do not use damaged or unknown batteries.
Conclusion
There are advantages and disadvantages to both the 18650 vs 21700 batteries. The 18650 battery is a smaller, cheaper, and popular battery that is suitable for daily use in various devices. With its increased capacity, runtime, and power delivery, the 21700 battery is perfect for today’s high-performance applications.
The bottom line is that it really depends on the individual, and different people may have different preferences. When it comes to a compact or older battery for smaller devices, 18650 is typically the safer of the two options to go with. For higher power and longer battery life, if applicable to your device, a 21700 battery may be the right choice.
