26650 Battery - Dimensions, Chargers, and Flashlights
Lithium-ion 26650 batteries are a common choice for high drain devices that also require large-capacity batteries, low self-discharge rate, and a large number of charging and discharging cycles. Lithium-ion 26650 rechargeable batteries are very similar to 18650 batteries, but they have ~2x larger volume and hence larger capacity/larger drain currents.
The most important features of 26650 rechargeable batteries are their native capacity, maximum pulse current, continuous drain current, maximum allowed charging current, protective electronics available, exact chemistry, and similar.
Updated: May 3, 2022.
26650 Battery Dimensions
26650 batteries size is standardized and it is:
- 26.5 mm (1.04 inches) in diameter, or ~26 mm.
- 65.4 mm (2.57 inches) in length, or ~65 mm.
Note that actual length may vary from the manufacturer to the manufacturer due to the fact that some models also feature protective electronics, button-type positive side, if the battery is rewrapped, etc.
The most important features of 26650 batteries are their capacity, voltage, charging/discharging performances, a number of charging/discharging cycles, and similar, and all of them depend mainly on the battery chemistry and internal design.
26650 Battery Chemistry
Like 18650 batteries, lithium 26650 batteries can be found in the most common lithium-ion versions:
- IMR 26650 batteries feature Lithium Manganese Oxide (LiMn204) chemistry with a nominal voltage of 3.6 - 3.7 V per cell and the maximum recommended charging voltage of 4.2 V.
IMR batteries commonly have smaller capacity when compared with other chemistries, but are capable of delivering stronger currents without adverse effects on the battery longevity.
IMR 26650 batteries commonly feature 5000 mAh (5 Ah) capacity and they are able to easily deliver 20 Amps continuously, 30 Amps with additional cooling, and 50-60 Amps pulse current. Of course, such features vary from model to model and must be checked for every different battery model.
- INR 26650 batteries feature Lithium Manganese Nickel (LiNiMnCoO2) chemistry. INR lithium-ion batteries are very similar to IMR batteries, they also feature 3.6-3.7 volts nominal voltage per single cell, 4.2 volts maximum charging voltage, etc. Also, they can provide large discharging currents, have slightly lower capacity, but also feature a larger number of charging/discharging cycles, lower self-discharging rate, etc.
When an INR battery is combined with protective electronics, one gets a 26650 lithium-ion battery that is very safe to use, has a capacity up to 5000 mAh, and is able to provide 20-30 Amps easily.
- IFR 26650 batteries feature Lithium Iron Phosphate (LiFePO4) chemistry and they feature a nominal voltage of 3.2 - 3.3 V per cell, with the maximum, recommended charging voltage of 3.5 - 3.6 V. IFR 26650 batteries are not very common.
- ICR 26650 batteries feature Lithium Cobalt Oxide (LiCoO2) chemistry with a nominal voltage of 3.6 - 3.7 V per cell, and with the maximum recommended charging voltage of 4.2 V. Their maximum allowed discharge currents are often limited to just a few C, but their capacity is larger when compared with other lithium-ion 26650 batteries.
Note: there are other chemistries available, including hybrid technologies like Lithium Nickel Cobalt Oxide (LiNiCoO2), Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2), etc.
Also, some manufacturers produce non-rechargeable Lithium Thionyl Chloride batteries in Size C (~26x50 mm) and advertise them as Size C batteries with or without a special battery holder/plug when used as 26650 battery replacement.
These batteries feature a large capacity even up to 9-10 Ah, good shelf life, good tolerance to cold and hot weather, low self-discharge rate, and are used mostly in security systems and EDC devices like flashlights and similar.
Flat or Button Positive (Top) Side/Terminal
Just like 18650 batteries, 26650 batteries also come with two different top (positive) sides: flat or button.
When replacing old 26650 batteries, it is very important to use new batteries that can fit the battery compartment of the device that you have, that discharging and charging features are the same (or better) and that the positive terminals are the same.
If the positive terminals (positive side) of the new batteries are not the same, there is a great chance that the new battery simply will not fit the battery compartment or that it will fit, but it will not be able to achieve proper electrical contact.
Protected or Unprotected 26650 Batteries
Protected 26650 batteries feature a small protective electronics system that monitors the parameters of the battery including battery temperature, charging and discharging currents, and voltages.
Protected 26650 batteries feature a slightly smaller capacity, but they are much safer to use in non-intelligent devices that don't monitor batteries' conditions during discharge.
When the charging/discharging conditions of the battery reach a certain threshold, protective electronics shut off the battery - it disconnects the battery from the rest of the world until the conditions are not returned to the acceptable range.
For example, if the battery voltage reaches 4.2 volts (if the 4.2 volts is the maximum allowed voltage), protective electronics will stop the charging process. If the discharge temperature reaches a certain threshold, protective electronics simply disconnect the battery until it cools down, etc.
Personally - regardless of the device you have, 26650 batteries with protective electronics are highly recommended. After all, it is IMHO better to sacrifice 200-400 mAh of capacity and have a safe battery than to risk fire, explosion, or similar accident due to the battery's thermal runaway ... Just my 2c :)
Rewrapped 26650 Batteries
High-quality 26650 batteries do cost some decent money, but they offer the best performances in terms of capacity, discharge current, a number of supported charging/discharging cycles, etc.
However, there is a large number of rewrapped 26650 batteries with exaggerated capacity and other battery features, which are not as safe as they should be.
So, when trying to find a proper 26650 battery, go for the batteries that have excellent reviews from other users, are made by just a few recommended brands that actually make 26650 batteries, or go for a high-quality 18650 batteries with a special battery holder, and use it as 26650 battery with somewhat lower capacity.
26650 vs 18650 Batteries
26650 and 18650 batteries are available in the same chemistries and feature practically the same length.
But, due to the larger diameter (~26 vs 18 mm), 26650 batteries feature ~2x larger volume and hence larger capacity, sometimes even more than 2x larger.
On the other hand, 18650 batteries are present on the market for a very long time and are sometimes easier to find.
Should You find yourself in the situation that You need a 26650 battery, go for high quality 18650 battery and use a battery holder that enables the user to place the 18650 battery in the 26650 battery compartment.
This battery swap works well in many devices, just be aware that the 18650 battery features a smaller capacity, and depending on the battery chemistry and design, it may also feature a weaker maximum discharge current.
26650 Battery Chargers
Most 26650 batteries can be and should be charged using intelligent battery chargers that are able to test the battery and determine its type, size, capacity, condition, etc.
Such battery chargers are relatively cheap and safe for use and often can charge NiCd, NiMH, and lithium-ion batteries, regardless of their chemistry and size.
Such battery chargers can be plugged into the wall power socket, and car cigarette lighter adapter, some even support the use of USB ports, but at the price of longer charging, etc.
Note: some 26650 batteries, just like similar 18650 batteries, feature a micro-USB (or some similar, standard) port, allowing the battery to be connected and charged directly from the USB ports.
Their capacity is usually lower than the capacity of standard 26650 batteries, but they don't require a dedicated battery charger - recommended battery type for people requiring just a few 26650 batteries.
The Best 26650 Battery Flashlights
26650 batteries are commonly used in high drain devices like toys, flashlights, vaping, etc.
26650 flashlights use 1 to 4, sometimes even more 26650 batteries and are able to produce 3000-4000 lumens of light per single 26650 battery, sometimes much more.
Such LED flashlights generally come with protective electronics that monitor the condition of LED(s), battery (or batteries), and if required decrease the light output and if absolutely required, shut off the flashlight until it cools down.
26650 flashlights are used as tactical flashlights, as EDC (Every Day Carry) flashlights, in emergencies, for outdoor activities, etc.
Long Story Short: 26650 batteries store plenty of energy, ready to be used at a moment's of notice. The most common battery types are IMR and INR, with the most intelligent chargers being able to distinguish between them and being able to charge them properly.
Protected 26650 batteries are by far safer than unprotected 26650 batteries, but they also feature a somewhat smaller capacity.
When going for the new 26650 battery/batteries, be sure to know what kind of new battery you actually need (voltages, currents, capacity, etc.).