Wuben Flashlight News

Basic knowledge of 18650 and 21700 rechargeable batteries

Dec 30, 2022

Basic knowledge of 18650 and 21700 rechargeable batteries


How much do you know about the 18650 and 21700 rechargeable batteries that you often see in wuben product descriptions? What is the difference between a 18650 rechargeable battery and a 21700 rechargeable battery? Today I would like to introduce the basic knowledge.

The 18650 rechargeable battery has a wide range of applications and a long history, so it is a battery with a considerably high technical level, but it tends to get hot when used for a long time, and the configuration is a bit complicated, and the fast charging is difficult. The problems have become more and more important. The 21700 rechargeable battery was born to improve these problems. The 21700 batteries are becoming more popular in the market today.


21700 rechargeable battery

As you all know, the 21700 rechargeable battery was originally developed by Panasonic for Tesla. Serial production began in 2017 and was placed on the market and immediately became popular enough to still be widely used.

As mentioned above, 21 stands for diameter, 70 stands for length, and 0 stands for a circular battery. Originally, the 21700 rechargeable battery was developed for electric vehicles to achieve better range. Therefore, even with the same amount of material, the 21700 rechargeable battery has a 35% higher capacity than the 18650 rechargeable battery and can be used for a long time.

What is the most interesting point of the 21700 rechargeable battery?

1、A large capacity

 The 21700 rechargeable battery has 3000-4800mAh, which is up to 35% improvement compared to the 18650 rechargeable battery's 1200-3600mAh.

2、Energy density

The energy density of the 18650 rechargeable battery is about 250Wh/kg, while that of the 21700 rechargeable battery is about 300Wh/kg, which is about 20% higher. Like the discharge capacity, a battery with a high energy density will have a longer continuous use time.


18650 rechargeable battery

Originally, 18650 rechargeable batteries referred to nickel metal hydride rechargeable batteries and lithium-ion secondary batteries. However, nickel metal hydride rechargeable batteries have not been adopted in many products due to the memory effect. Currently, 18650 batteries are generally regarded as a standard type of Li-ion secondary battery. 18 means diameter (millimeters), 65 means length (millimeters) and 0 means circular battery. Usually, a protective circuit is mounted on the battery body (cell) and the length is between 67 and 69 mm. The main battery voltage is 3.7V and the capacity is 2500-3500mA.

What are the characteristics of the 18650 rechargeable battery?

1、Can be recharged and used repeatedly

Manganese batteries and alkaline batteries, called dry cell batteries, must be discarded when they are dead. However, Li-ion batteries can be charged and used and can withstand more than 500 charge/discharge cycles.

2、Large capacity

 A normal battery has a discharge capacity of around 800mAh, while a 18650 battery can reach 1200-3600mAh. Simply put, the role of unloading capacity is that the larger the unloading capacity, the longer the running time. The 18650 battery can keep 80% capacity even after one month if it is fully charged, and it can be used as an emergency power source depending on how it is used.

3、Compact but high voltage

The nominal voltage is 3.7V, which is 2.5 times the voltage of a so-called dry cell (1.5V). Although it is small, it has a large capacity and a long life compared to dry cell batteries, so it is widely used as a battery for portable products such as smartphones and flashlights.


 Below is table for comparison of 21700 vs 18650






Diameter 18mm



Length 65mm


Diameter 21mm



Length 70mm



Flashlight with 18650 rechargeable battery




Flashlight with 21700 rechargeable battery

Leave a Comment

Your email address will not be published.