Battery Equivalents and Replacements

Best 21700 Battery

Lithium-ion 21700 batteries are very popular 3.6-3.7 volts batteries for high drain devices that also require long-lasting batteries in terms of constant voltage, battery capacity, low self-discharge rate, and a large number of charging and discharging cycles.

21700 lithium rechargeable batteries come in many versions differing in their chemistry, battery capacity, maximum pulse, and continuous drain current, maximum charging current, protective electronics, battery terminals, etc.

samsung inr21700 30t battery 2

21700 Battery Features and Specifications

Rechargeable lithium-ion 21700 batteries are a common choice for high drain devices requiring high capacity battery packs, including high power flashlights, electric bikes, scooters, and other vehicles, high-end toys, cordless tools, drones, etc.

21700 battery official dimensions are (diameter x length) 21 × 70 mm (0.827 x 2.756 inches), although actual dimensions slightly differ from model to model, but these small variations in size usually make no problems - keep in mind that button top batteries may be slightly longer.

Before replacing your old 21700 batteries, there are a few things to consider first.

The capacity of the 21700 batteries varies, and it is usually in the 3000 - 5000 mAh range, depending on the model, design, and exact chemistry.

Charging and discharging currents depend on whether the 21700 battery is a high or low-drain battery. High-drain 21700 batteries sometimes may provide huge currents (30+ Amps easily) without adverse effect on the battery longevity, while low drain 21700 batteries should not be discharged with more than, for example, 5 Amps. But, high drain 21700 batteries usually feature capacity in the 3000-4000 mAh range, while low drain 21700 batteries have the capacity in the 5000+ mAh range.

Protected 21700 batteries - since rechargeable lithium-ion batteries are sensitive to charging and discharging currents (always use dedicated lithium battery charger!), temperature, voltage, and similar, some 21700 batteries feature built-in protective electronics (Battery Management System - BMS), which monitors parameters of the battery like charging current, discharging current, voltage, temperature and similar, and if required protects the battery by shutting it off until conditions change - battery cools down, no more short circuit, etc.

Battery Management System (BMS) occupies some space within the battery slightly decreasing the capacity of such batteries.

Note: unless your device features some sort of Battery Management System, go for protective 21700 batteries - better safe than sorry.

Flat or button positive (top) battery terminal - there are two versions of positive (top) 21700 battery terminal: flat top and button top.

samsung inr21700 30t battery fenix arb l21 21700 battery

Some of the devices being powered by 21700 batteries support the use of both battery types, but just to be sure check the documentation of your device or go for the type that is already working well within your device.

Note: the actual length of the button top 21700 batteries may be slightly longer than the standard length of 70 mm - manufacturers measure the length of the battery's body, but the button top adds 1-2 mm more. This '1-2 mm' usually is not of an issue, but it may be ...

21700 Battery Chemistry - IMR, INR, IFR, or ICR 21700 Batteries

Labels of 21700 batteries often include abbreviations like IMR, INR, IFR, or ICR. These abbreviations describe actual battery chemistry:

- IMR 21700 batteries feature LiMn204 (Lithium Manganese Oxide) chemistry. Their nominal voltage is 3.6 - 3.7 V per cell, with a maximum recommended charging voltage of 4.2 V. IMR batteries commonly have a relatively smaller capacity but are capable of delivering large currents.

- INR 21700 batteries feature LiNiMnCoO2 (Lithium Manganese Nickel) chemistry. These batteries are very similar to IMR batteries, they can provide plenty of currents, with again, slightly lower capacity.

- IFR 21700 batteries feature LiFePO4 (Lithium Iron Phosphate) chemistry. Their nominal voltage is 3.2 - 3.3 V per cell, with the maximum recommended charging voltage of 3.5 - 3.6 V. Despite having lower voltage and often 'just' a modest capacity, IFR batteries are very safe batteries, often used in electric bikes/scooters and similar vehicles and power tools without protective electronics.

- ICR 21700 batteries feature LiCoO2 (Lithium Cobalt Oxide) chemistry. Their nominal voltage is 3.6 - 3.7 V per cell, with the maximum recommended charging voltage of 4.2 V. They commonly have higher capacities, but maximum allowed currents are often limited to just a few C.

Note: there are other chemistries on the market too, including hybrid technologies like Lithium Nickel Cobalt Oxide (LiNiCoO2), Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2), etc.

Most Popular 21700 Batteries

With all sorts of devices being powered by 21700 batteries, it is somewhat difficult to judge which 21700 battery is actually 'the best' one. Here is our list of 21700 batteries with their most important features, so choose 21700 batteries according to your own needs and preferences.

After all, it is not the same if You have, for example, an electric scooter or similar unit/device requiring 20 or more peek Amps, or You have a 21700 LED flashlight, requiring constant 3-4 Amps of current.

Samsung 40T 21700 Battery

Samsung 40T 21700 battery is a high-drain INR lithium-ion battery, featuring 4000 mAh capacity when being discharged at 0.2C (800 mA) down to 2.5 cut-off voltage.

samsung inr21700 40t battery

Its standard charge current is 0.5C (2 Amps) with a voltage of up to 4.20 volts.

Samsung 40T 21700 battery is an unprotected 21700 battery and should be used in devices that monitor battery condition.

The maximum continuous discharge current is 35 Amps without the temperature cut and 45 Amps with 80°C surface temperature cut - these are large currents, and not many batteries can handle them safely.

Also, not many devices require their 21700 batteries to work that hard.

Very similar Samsung 30T 21700 battery features similar output currents, but it also has a somewhat lower capacity of 3000 mAh - for constant discharge currents of 25 Amps or more, Samsung 30T is the preferred model, while below 25 Amps and especially below 20 Amps, Samsung 40T is a better performer.

In short, Samsung 40T 21700 battery can provide ample power and still features a very good capacity for powering low drain devices.

 Golisi S35 21700 Battery

Golisi S35 is another very interesting model of high-drain 21700 battery.

golisi imr 21700 s35 batter

Golisi S35 is based on the IMR chemistry and features 3750 mAh nominal capacity and a maximum constant discharge current of 30 Amps!

When the battery is not pushed to its limit, the user may expect up to 800 charging/discharging cycles, and that is a lot for a hard-working battery.

iJoy 21700 3750 mAh Battery

iJoy 21700 3750 mAh battery is a rather affordable high-drain battery featuring decent capacity.

ijoy 21700 battery

Although the iJoy 21700 3750 mAh battery is labeled as being able to provide 40 Amps, the battery performs overall much better when the constant discharge currents are kept down to 25 Amps, preferably below 20 Amps.

iJoy 21700 3750 mAh battery is a reliable 21700 battery, just don't push it as hard as Samsung 40T, Samsung 30T, or Golisi 35S.

Of course, there are other high-drain 21700 batteries on the market, but these are the most popular 'best buy' models.

Fenix ARB-L21-5000 21700 Battery

Fenix ARB-L21-5000 21700 battery is 3.6 volts 5000 mAh high-capacity 21700 battery, designed for high-drain LED flashlights.

fenix arb l21 21700 battery

Fenix ARB-L21-5000 21700 battery is a button-top 21700 battery fitted with protective electronics that monitors the most important parameters of the battery (temperature, overcharge, over-discharge, short circuit).

In order to protect the battery from mechanical impacts and damage, Fenix ARB-L21-5000 21700 battery features a steel shell.

Important Note: Fenix ARB-L21-5000 21700 battery is intended for high-drain flashlights like excellent Fenix PD36R 1600 Lumen EDC Tactical Flashlight (Amazon link, link opens in the new window), but the battery itself is NOT high-drain 21700 battery!

Olight ORB-217C50 INR 21700 Battery

Olight ORB-217C50 is another high-capacity 21700 battery featuring 5000 mAh nominal capacity.

olight orb 217c50 battery

Olight ORB-217C50 INR 21700 battery is intended for powering high-drain flashlights and similar devices and offers long shelf life (excellent for EDC flashlights and other standby devices), a large number of charging/discharging cycles (drain/device dependent) etc.

Again, Olight ORB-217C50 INR 21700 battery is not a high-drain 21700 battery, but it is intended for high-drain flashlights and similar units - that is a big difference! Some of the most popular uses of the Olight ORB-217C50 INR 21700 battery are Olight Seeker 2 Pro 3200 Lumens Tactical Flashlight and OLIGHT M2R Pro Warrior 1800 Lumens Tactical Flashlight (Amazon links, links open in the new windows).

There are other models of high-capacity 21700 batteries suitable for different uses, but these models perhaps offer the most, considering their price.

How to Charge 21700 Battery

Every 21700 battery comes with a slightly different 'optimal' charging current, but general rules apply and they are not about 'optimal' charging current, but about safety.

Always, but really always charge 21700 batteries with intelligent lithium-ion battery chargers intended for such batteries, or these batteries may burst into flames or even explode - this is not 'just another' warning, this is a serious warning.

These batteries stores plenty of energy considering their size and if mistreated, they can 'fight back'.

Thus, charge them with lithium-ion chargers intended for 21700 batteries and if possible, use 21700 batteries with built-in protective electronics - better safe than sorry!

Best 21700 Battery Frequently Asked Questions (FAQ)

Here are some of the most common questions about the 21700 batteries, their chargers, flashlights that use 21700 batteries, and similar.

Are 21700 batteries safe?

21700 batteries are as safe as any other similar lithium-ion battery - in order to be actually safe, it has to feature a built-in Battery Management System (BMS) that monitors the condition of the battery and prevents unwanted events from occurring.

How long does a 21700 battery last?

It all depends on the actual meaning of the word 'last' - when not in use, 21700 batteries should be recharged every 3-6 months.

Also, they support a few hundred charging/discharging cycles down to 100% DOD, although there are 21700 batteries that support thousands of charging/discharging cycles - chemistry dependent.

In the end, how long they "last" depends on the discharge conditions.

Are 21700 batteries better than 18650? Does 21700 last longer than 18650?

Generally, 21700 batteries are larger than 18650 batteries and feature larger capacity, and support stronger charging/discharging currents.

Of course, high-discharge 18650 batteries can provide stronger currents than low-discharge 21700 batteries, but low-discharge 21700 batteries feature larger capacity than low-discharge 18650 batteries and much larger capacity than high-discharge 18650 batteries.

How much does a 21700 battery cost?

The actual price depends on the brand, chemistry type, battery quality, supported number of charging/discharging cycles, etc.

Do 21700 batteries fit 18650? Do 18650 batteries fit 21700?

No, 21700 batteries don't fit the 18650 battery compartment. Also, 18650 batteries don't fit 21700 battery compartments.

However, if required, it is possible to purchase 18650 to 21700 battery adapters, allowing the users to place 18650 batteries into the 21700 batteries compartments.

Such adapters allow the users to more easily find batteries for their devices, just be aware that 18650 batteries are smaller and have smaller capacities.

Can a 18650 charger charge 21700?

Some 18650 battery chargers accept both larger and smaller batteries than the 18650 batteries, 21700 batteries included.

How to charge a 21700 battery?

The easiest way is via lithium battery chargers that support charging of the 21700 batteries.

Some 21700 batteries come with micro-USB charging ports, allowing the users to charge them directly from the USB ports found on laptops, desktops, and similar devices.

How big is a 21700 battery?

The physical dimensions of the 21700 batteries are (D x H) 21 x 70 mm.

Does Tesla use 21700 batteries?

Yes, after using 18650 batteries on the Model S and Model X, the 21700 batteries are used in the Model 3, for example.


Long Story Short: 21700 batteries are relatively large lithium-ion rechargeable batteries, being able to store plenty of energy and release it when required.

Regardless of the exact chemistry type, 21700 batteries should feature a built-in Battery Management System (BMS), or they should be a part of an electric system that already features such safety system.

When looking for 21700 batteries, always go for the models from reputable brands with plenty of good reviews - such models have already been tried and tested by numerous users in the real-life situations.

And, whatever You do, stay safe.