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 large number of charging and discharging cycles.
21700 lithium rechargeable batteries come in many versions differing in the their chemistry, battery capacity, maximum pulse and continuous drain current, maximum charging current, protective electronics, battery terminals etc.
21700 Battery Features and Specifications
Rechargeable lithium ion 21700 batteries are 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 few things to consider first.
Capacity of the 21700 batteries varies, and it is usually in the 3000 - 5000 mAh range, depending on the model, design and chemistry.
Charging and discharging currents depend if the 21700 battery is 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 has 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 feature 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.
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: actual length of 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 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 maximum recommended charging voltage of 4.2 V. IMR batteries commonly have 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 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 battery according to your own needs and preferences.
After all, it is not the same if You have, for example, electric scooter or similar unit/device requiring 20 or more peek Amps, or You have 21700 LED flashlight, requiring constant 3-4 Amps of current.
Samsung 40T 21700 Battery
Samsung 40T 21700 battery is 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.
Its standard charge current is 0.5C (2 Amps) with the voltage up to 4.20 volts.
Samsung 40T 21700 battery is unprotected 21700 battery and should be used in devices that monitor battery condition.
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 somewhat lower capacity of 3000 mAh - for constant discharge currents of 25 Amps or more, Samsung 30T is preferred model, while below 25 Amps and especially below 20 Amps, Samsung 40T is better performer..
For short, Samsung 40T 21700 battery can provide ample of power and still features 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 S35 is based on the IMR chemistry and features 3750 mAh nominal capacity and 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 hard working battery.
iJoy 21700 3750 mAh Battery
iJoy 21700 3750 mAh battery is rather affordable high-drain battery featuring decent capacity.
Although iJoy 21700 3750 mAh battery is labeled as being able to provide 40 Amps, 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 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-L21-5000 21700 battery is 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 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 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), large number of charging/discharging cycles (drain/device dependent) etc.
Again, Olight ORB-217C50 INR 21700 battery is not 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 offers the most, considering their price.
How to Charge 21700 Battery
Every 21700 battery comes with 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!