21700 Battery Guide
Lithium Ion 21700 Cells
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What is a 21700?
At it’s most basic an 21700 is a Li-Ion (Lithium Ion) cylindrical cell that uses its dimensions as it’s designation. The first two digits are the approximate diameter, in this case 21mm and the following 3 digits are the approximate height in tenths of millimeters, in this case 70mm. Hence the 21700 designation. These cells have a nominal open circuit voltage of 3.7V per cell and a full charge voltage of 4.2V. 21700 cells have been used for some time in cars, electric bikes, vapes and numerous other battery pack applications. However, they are increasingly finding there way into more and more diverse consumer devices such as high powered LED torches. Some of the advantages of Li-Ion include a high energy density, low maintenance, low self discharge rates and depending on the cell a high maximum continuous discharge rate.
“PCM” or “BMS”
Generally Li-Ion cells in most consumer devices will have a protection circuit module (PCM or PCB). The PCM will help to protect the cells or battery pack from over charging, over discharge and over current and short protection. The PCM will help protect the user from potential fire and explosion. A battery management system (BMS) is a similar circuit, with far more features. A BMS can or may monitor such things as the batteries charge state, balance the battery, report data, temperature, voltage, state of health. It is extremely important to use caution when working with and using lithium ion batteries as they are very sensitive to charging characteristics and may explode, burn, or can cause a fire if misused or mishandled. We highly recommend reading our Li-Ion precautions sheet on handling Li-Ion.
What is the difference between an 18650 and a 21700?
What is the difference between a 21700 battery and an 18650 battery? Essentially, the only physical difference is the size. 21700 cells are slightly larger than 18650 batteries. With the increase in size, there is also an increase in capacity or energy/power. Generally, the capacity, or mAh (milliamp hours), ranges from 3000mAh up to 5000mAh. There are some unreputable 18650 cell brands that advertise capacities of up to 9000mAh. However, these claims are often inaccurate, and they cannot deliver that power, if you are at all unsure you can contact us to discuss it. We will supply and recommend only reputable cell manufacturers
How do I select an 21700?
There are many different types of Li-ION (Lithium-Ion) cells available, all designed to do a different job and generally differentiated by the chemical abbreviation, 6 of the most common are listed below:
- LiCoO2 (Lithium Cobalt Oxide – LCO)
- LiMn2O4 (Lithium Manganese Oxide – LMO)
- LiNiMnCoO2 (Lithium Nickel Manganese Cobalt Oxide – NMC)
- LiNiCoAlO2 (Lithium Nickel Cobalt Aluminum Oxide – NCA)
- Li2TiO3 (Lithium Titanate – LTO)
- LiFePO4 (Lithium Iron Phosphate – LFP)
Selecting the right Li-ION cell for your job comes down to a number of different factors depending on what you want the 21700 to do. Do you want to be able to discharge a high current in a short burst, or does your 21700 need to deliver a long cycle life? Lets take a look at some of the best quality cells on the market and some of their key features.
21700’s Available
SAMSUNG INR21700-40T 4000mAh Battery
The SAMSUNG INR21700-40T is a high capacity 4000mAh cell, with a high maximum continuous discharge rate of 35A. This is one of the best 21700 cells on the market, striking a great balance with very high capacity, whilst also having Ultra-High Discharging/Drain capabilities without any compromise.
SAMSUNG INR21700-50E 5000mAh Battery
The SAMSUNG INR21700-50E is a high capacity 5000mAh cell, with a maximum continuous discharge rate of 9.8A to 60 Deg. C. The cell is ideal for applications such as E-Bikes, scooters and other medium to high drain applications.
LISHEN LR2170SA 4000mAh Battery
The LISHEN LR21700A is a medium rate capacity 4000mAh cell, with a maximum continuous discharge rate of 12A. The cell is a great cost effective alternative to the SAMSUNG INR21700-50E, if you don’t need quite as high capacity.
More 21700 Cells Available Soon, Watch This Space
Capacity & Discharge Rates Chart
To make this easier for you we have listed some of the most common 21700 cells available on the market. The following chart can be sorted by the capacity, maximum continuous discharge rate or brand.