21700 vs 18650 Battery – What’s the Same, What’s Different
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What is the difference between a 21700 vs 18650 Battery?
Short Answer: A “standard” 21700 is big, 47% bigger by volume than an 18650. It is about 50% heavier than a “standard” 18650. Because it is bigger it can store roughly 30% to 50% more power measured in mAh or amp hours. Both are rechargeable 3.6v batteries.
The largest 18650 stores about 3.6Ah (amp hours) vs the largest 21700 storing about 5.1Ah or a maximum of about 42% more energy (amp hours or mAh).
Table of contents
Similarities between 21700 and 18650
Both the 21700 cells and 18650 cells are high capacity rechargeable 3.6volt batteries. The common battery cell material (chemistry) for both is Li-ion (Lithium Ion).
- Used in power tools, flashlights, some toys, electric vehicle battery packs, laptops and other battery packs.
- May come in button top or flat format.
- Have good energy density, meaning amount of power per gram or ounce.
- Tend to be used in high drain devices such as: vapes, battery packs, power tools and electric vehicles.
- Are cylindrical cells .
- Both have similar low self discharge rates – they do no lose power quickly when the battery is not being used.
- Can be recharged many times, likely over 500 times.
- Have similar operating temperatures roughly -20°C to +50°C (-4°F to + 122°F) the optimal temperatures is 25°C (77°F)
Specs Comparison 21700 vs 18650
Comparing the Nitecore 21700 Battery to the Nitecore 18650 Battery
| Nitecore 21700 | Nitecore 18650 | |
| Voltage | 3.6v | 3.6v |
| Capacity (higher is better) | 5000mAh 18Wh | 3400mAh 12Wh |
| Chemistry | Lithium Ion | Lithium Ion |
| Diameter | 0.85in (21.6mm) | 0.74″ (18.7mm) |
| Length | 2.96in (75.2mm) | 2.73″ (69.3mm) |
| Weight | 2.57oz (73g) | 1.7oz (48.2g) |
| Recharge Times | 500 times | 500 times |
| Battery Cost* | $24.95 | $18.95 |
| Cost per 1000mAh | $4.99 | $5.57 |
*Battery prices will change regularly. This is a point in time comparison.
This is a comparison of a NiteCore 21700 5000mAh battery and a NiteCore 3400 mAh 18650 battery. The 21700 has 30% to 50% more capacity (mAh), weighs 50% more and is up to 20% cheaper per 1000mAh. This is just two batteries but still gives you a rough idea of the differences.
Which is best the 18650 vs 21700?
There is not a “best”. The type of battery you pick needs to match the usage. A battery powered device that uses an 18650 needs 18650s, a device that uses 21700s needs 21700s.
If you are deciding between flashlights or vaping devices, the overall weight and functionality are more likely more important than the specific battery type. In general though, if runtime is important, the 21700 is better. It has more power, so the device will likely run longer than an 18650.
With equal load (power draw) an 21700 will last 30% to 47% longer than an 18650 lithium ion battery.
If you are choosing batteries, generally select the higher capacity of either battery, the 5000mAh 21700 batteries or the 3500mAh 18650 batteries.
The energy density of the 21700 is up to 300WH/kg and the 18650 energy density is up to 250Wh/kg.
21700 and 18650 Best Brands
The best brands for 21700 and 18650 batteries include: Samsung, Nitecore, Olight, Klarus or LG. We have used batteries from these brands and they are reliable.
Cost Comparison Details
The prices per amp hour are similar for the 18650 and 21700, but they do vary a lot so you need to shop around.
Prices for either type of battery will vary based on supply chain, demand, supply, sales and new technology. The comparison used December 2022 prices.
Currently costs per mAh are about the same for UNPROTECTED 21700 and 18650 batteries but the prices for PROTECTED 21700 and 18650 much more. The PROTECTED 21700 can vary from 20% cheaper to 40% more expensive per mAh compared to PROTECTED 18650 batteries.
Capacity (Energy Storage) Details
A 21700 battery can store between 15% to 52% more energy than an 18650. In a perfect world with two max capacity batteries, the 21700 stores 47% more than the 18650. But beware, some of the better 18650s can store more energy than a poor 21700, so pay attention to the details.
- 18650 capacity range 2200mAh to 3600 mAh
- 21700 capacity range of 3300 up 5100 mAh
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Size Details
The 21700 is 25% bigger than the 18650. The 21700 is wider and longer, 21mm by 70mm. The smaller 18650 is 18mm by 65mm.
Weight Comparison
The 21700 is 40% to 90% heavier than an 18650. Generally heavier means more capacity but not always. A 21700 battery should weigh between 60g (2.1oz) and 75g (2.6oz) and an 18650 should weigh between 42g (1.4oz) to 47g (1.6oz)
The materials used to create the battery can cause wide differences in the weight of a battery. A Li-Po battery is far lighter than an Li-Ion battery of the same capacity. Currently Li-Po 18650 or 21700 are not readily available. Other chemistry such as Ni-Zn may become more common.
Protected vs Unprotected Mode
Protected mode batteries or simply referred to as “PROTECTED” batteries have an overcharge and overdraw circuit to protect from fire or bursting.
A Protected battery has a tiny Internal PCB (protection circuit board). The PCB prevents under-voltage during DRAW and over-voltage during CHARGE. Use unprotected batteries only in a device that has its own overdraw and overcharge.
We recommend that you purchase 21700 and 18650 protected batteries. The cheapest of both the 21700 and 18650 are UNPROTECTED. Unprotected batteries do work, but pose a fire or burst risk if the device, charger and/or use overdraws or overcharges the battery.
21700 vs 18650 Battery Charger
In most cases the charger, such as the Nitecore UMS4 Battery Charger will work for either the 21700 or 18650. We like the UMS4 because it can use almost any power source that can power USB.
A charger with higher wattage will take less time to charge the batteries, but generally those require direct AC power.
Tips when purchasing 18650 or 21700 Batteries
Capacity: If you see anything above 3600mah for an 18650 Battery or above 5100mah for a 21700 battery be suspicious. It is likely false advertising.
Protected vs Unprotected: Make sure you are comparing a PROTECTED or UNPROTECTED lithium ion cell. The electronics of the PROTECTED batteries adds cost. If it is really cheap it might be UNPROTECTED and not say it.
Weight Tip: If a 21700 weighs less than 60g or an 18650 weighs less than 42g it is likely not good quality or is a knock-off (fake).
Source: Buy from reputable source and name brand manufacturer.
Shop Around: Always compare costs before you purchase. An 18650 or 21700 could be on sale, in high demand or out of stock somewhere and make a big difference in price.
Test: When buying 18650 or 21700 batteries – buy ONE before you buy multiple in case the size is not 100% correct. Some cheaper manufacturers don’t entirely follow the 18mm x 65mm and 21mm x 70mm specification. Even reputable manufacturers batteries may be consistently larger or smaller.
Be Suspicious: If it looks too good to be true, it probably is.
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This post was written by August Neverman IV. August has a strong background in emergency preparedness. He served on several emergency preparedness teams during his tenure at Brown County WI Government, the Medical College of Wisconsin, HSHS, a 13-hospital system and emergency response training during his time with the Air Force and Air National Guard. Learn more about August.