Battery Technologies. 18650 lithium battery voltage

Learn About 18650 Lithium-ion Batteries

As far as LED flashlights go, most users will tell you that a light which primarily runs on a 18650 battery is usually the preferred choice. Therefore, I predict this discussion on 18650 Lithium-ion batteries to be quite informative.

Where Did The Name Come From?

All lithium-ion batteries get their numeric identifiers from their size. In the case of a 18650, (for instance) it’s 18mm in diameter and 65mm long. The zero at the end simply means it’s cylindrical. Some 18650’s will differ in length…but only slightly. The difference is with those that are “protected”.

What’s This “Protection” Stuff About?

This means that a protection circuit has been physically added to the cell. This is preferred since it gives the battery added protection from being accidentally over-charged or over-discharged. If you’re given a choice of protected or unprotected, think of the protected cell as being an insurance policy against possible charging failures. Nominal voltage on a 18650 is 3.7 and shouldn’t be discharged below 3.0 in most cases. The added circuit will make certain that while being discharged in a flashlight, the cell’s voltage doesn’t go below that threshold. On the high end, a freshly charged 18650 Lithium-ion battery will normally peak at 4.2 volts.

What Does mAh mean?

A 18650 battery is a very powerful choice when it comes to operating an LED flashlight. A Lithium-ion’s available power is measured in milliamp hours (mAh). The higher the mAh capacity, the better. This ensures longer lasting power from the battery. Cells are marketed with capacities anywhere from 2100 all the way up to 3400mAh. Do yourself a tremendous favor by reading this article on the dangers of buying 18650 cells that are marketed at capacities ABOVE 3400mAh.

Pricey Little Devils!

When shopping for a 18650 battery, you may be surprised at the price tag. But what you’re paying for is a very durable and powerful piece of technology. Many of the LED flashlights made today can crank out up to one thousand lumens of light. To drive a flashlight hard enough to produce this level of light, you NEED a powerful battery! And most 18650 lights will only take ONE cell.

battery, technologies, 18650, lithium

Since these batteries are rechargeable, you’ll definitely get your money’s worth from them! Even though can easily reach up to 30, it’s worth it. You’re getting a quality made, dependable, long-lasting battery capable of hundreds of charging cycles.

I have many flashlights that operate on 18650 batteries and can tell you from personal experience that it’s a quality combination!

The photo is showing two different brands of 18650… EagleTac and Olight. As you can probably make out, the top one is 3.7 volts and the bottom battery is 3.6 volts. Operationally, there’s no difference between the two.

Please note that they’re often available in both button-top and flat-top versions. Protection circuits are included on both.

Flat-top cell on left; Button-top on right

Flat or Button Top?

In many situations, buying a button-top vs. a flat-top makes no difference. BUT, for some flashlights, depending on whether the battery tube features a spring, or a direct electronic connection to the head, it might be a tight fit. This is often due to the added protection circuit, not so much the style of battery. In other cases, the light in question might not work with a flat-top cell. I own a couple that won’t. Although this might be more of an exception, it’s often hit or miss when attempting to marry batteries and lights, and not finding out until the last second if they’re actually compatible!

Bottom line, when shopping for an LED light, pay close attention to the battery configurations recommended for that particular flashlight. Choosing one which accepts a 18650 Lithium battery will ensure many years of dependable service!

Looking to Buy?

It can be tricky shopping for 18650’s, and deciphering the GOOD ones from the BAD!

Therefore I’m suggesting you follow THIS LINK which will take you to an 18650 battery page at There are many VERY GOOD QUALITY cells at that page!! It’s much SAFER than buying them from Amazon!

What’s your opinion of this article?

Do you have additional questions, or perhaps some personal experience with lithium-ion that you’d like to share?

Please let me know in the Комментарии и мнения владельцев

Battery Technologies

There are a multitude of different battery technologies available. There are some really great resources available for the nitty gritty details behind battery chemistries. Wikipedia is especially good and all encompassing. This tutorial focuses on the most often used batteries for embedded systems and DIY electronics.

Suggested Reading

There are some concepts and bits of knowledge you may want to know before reading this tutorial:

What is Electricity?

We can see electricity in action on our computers, lighting our houses, as lightning strikes in thunderstorms, but what is it? This is not an easy question, but this tutorial will shed some light on it!

Alternating Current (AC) vs. Direct Current (DC)

Learn the differences between AC and DC, the history, different ways to generate AC and DC, and examples of applications.

Looking to explore different batteries?

Lithium Ion Battery. 400mAh

This is a very small, extremely lightweight battery based on Lithium Ion chemistry, with the highest energy density currently…

Coin Cell Battery. 20mm (CR2032)

CR2032 Lithium metal 3V 250mAh button cell battery. Great for powering low power processors or blink an LED for weeks at a ti…

Lithium Ion Battery. 18650 Cell (2600mAh)

No, these aren’t some sort of weird, AA battery, this is actually a 18650 Lithium Ion Cell. These round high capacity cells h…

9V Alkaline Battery

These are your standard 9 Volt alkaline batteries from Rayovac. Don’t even think about trying to recharge these. Use them wit…


Here are some terms often used when talking about batteries.

Capacity. Batteries have different ratings for the amount of power a given battery can store. When a battery is fully charged, the capacity is the amount of power it contains. Batteries of the same type will often be rated by the amount of current they can output over time. For example, there are 1000mAh (milli-Amp Hour) and 2000mAh batteries.

Nominal Cell Voltage. The average voltage a cell outputs when charged. The nominal voltage of a battery depends on the chemical reaction behind it. A lead-acid car battery will output 12V. A lithium coin cell battery will output 3V.

The key word here is nominal, the actual measured voltage on a battery will decrease as it discharges. A fully charged LiPo battery will produce about 4.23V, while when discharged its voltage may be closer to 2.7V.

Shape. Batteries come in many sizes and shapes. The term ‘AA’ references a specific shape and style of a cell. There are a large variety.

Primary vs. Secondary. Primary batteries are synonymous with disposable. Once fully-drained, primary cells can’t be recharged (reliably/safely). Secondary batteries are better known as rechargeable. These require another power source to fully charge back up, but they can fully charge/discharge many times over their life. In general primary batteries have a lower discharge rate, so they’ll last longer, but they can be less economical than rechargeable batteries.

Energy Density. Combining capacity with shape and size of a battery, the energy density of a battery can be calculated. Different technologies allow different densities. For example, lithium batteries typically pack more juice into a given volume than alkaline or coin cell batteries.

Internal Discharge Rate. Have you ever tried to start a car that has been sitting for 6 months? Batteries discharge when sitting on the shelf or when unused. The rate at which the battery discharges itself over time is called internal discharge rate.

Safety. Because batteries store power, they are basically very tiny explosives. To prevent harm, batteries are designed to be as safe as possible. Most batteries technologies are designed to discharge safely in the event of misuse. If you hook up an alkaline battery incorrectly, it may get hot to the touch but should not catch fire. Most Lithium Polymer batteries have safety circuits built-in to prevent damage to battery and prevent it from unsafe usage.

For a full list of terms and technical overview Wikipedia is an [excellent resource](

Lithium Polymer

Lithium Polymer (often abbreviated LiPo) batteries are very useful for embedded electronics. They offer the highest density readily available on the market. Because cell phones predominantly use this battery type, they are easy to find for reasonable prices. They do require special charging, so be sure to use the right charger for the job. SparkFun carries a variety of 3.7V Lithium Polymer batteries. many of which are listed below. The capacity of the battery you choose will depend on the intended run time of your project, size constraints, and other factors.

Facts about 18650 battery voltage. to better use and longer battery life

To talk about the battery voltage, the potential difference between the anode and cathode of the battery must be measured. The greater the potential difference, the greater will be the voltage of the battery and vice versa.

When we further understand the electric potential, it is the difference in charge between the two poles of a cell, one with a negative charge and the other with a positive charge.

When we discuss the voltage for battery pack, several cells are connected in series to make a battery pack and all cells have individual voltages which add up to make a nominal voltage of a battery pack i.e. 48v, 24v, 12v battery etc.

.What is the common 18650 battery voltage?

Voltage depends on the type and chemistry of the battery, as all 18650 batteries are Li-ion batteries that have a voltage range between 3.2v to 3.7v

And 18650 li-ion batteries are highly advanced with a BMS system which cuts off the overcharging and discharging of the battery,therefore, the battery voltage will not be too low or too high.

.Why does the 18650 battery voltage change during charge and discharge?

As you know the charging of the battery involves the supply of energy to the battery,and expenditure of energy is involved to discharge the battery.The voltage rises as the amount of electricity rises and falls as the amount of electricity falls.

In general, a battery will have a charge cutoff voltage and a discharge cutoff voltage, which are the upper and lower limits of the battery voltage, meaning that the voltage rises through charging from the low point to the maximum point, that is, the battery works between these two points.

Let’s know about voltage changes while charging and discharging. Consider your 18650 battery voltage is 4.2v when fully charged. When you connect a device or a bulb at this voltage point, energy is consumed by the bulb and charge is lost to some extent. The bulb is continuously on and the battery is also being discharged with the passage of time and the voltage is also decreasing due to decreasing in charge. Eventually, the bulb is dimmed when the battery is discharged till the BMS cut off the discharging. So the voltage also decreased to its lowest range.

As a lithium-ion battery, when the 18650 battery is charged, it experiences a process of constant current and constant voltage. In the previous stage of charging, the current is large and constant, and the voltage rises until the charging cut-off voltage. At this time, the voltage is constant, and the charging current slowly decreases, until the battery is fully charged.

.Is there a relationship between 18650 battery voltage and SOC?

To understand the relationship between voltage and SOC let’s use the voltage vs SOC chart in the 18650 batteries.

The voltage of lithium-ion batteries changes concerning the SOC (state of charge) of the battery which varies from 100% to 0% i.e. fully charged state to fully discharged.It is seen that a fully charged battery has maximum voltage while the drained one has the lowest range of voltage.

Although the voltage can be affected by factors like temperature and current etc. Voltage can be used to determine the state of charge of the battery. Now voltage translation is used vs the state of charge of the battery for an explanation.

Here the voltage is maximum at 100% and lowest at 0%. And voltage changes on both ends of the state of charge.

.What voltage is too low for the 18650 battery?

LiFePo4 18650 batteries with a maximum voltage of 3.65V and a minimum voltage of 2v. If the voltage is below this range, it can adversely affect its health.

These types of batteries are provided with a BMS system which prevents the battery to discharge below the lowest value of the voltage. It turns the sleep mode on to make the battery safer.

.Can I charge 18650 with a 5V charger? What is the best charge voltage for a 18650 battery?

You must notice the compatibility of both the battery and charger. The voltage range of the charger must be within the voltage range of the battery. A charger must be provided with a safety that would not allow the voltage to be exceeded the cut off voltage of the battery.So you must see the specification of the battery and charge the batteries with the appropriate charging current to their recommended value of voltage with their compatible charger.

Be careful of the cell chemistry. Different types of batteries need to use different chargers due to different charging modes, which is determined by their chemical properties. Therefore, as a lithium-ion battery, the 18650 battery must be charged with a dedicated CC-CV charger.

Some 18650 batteries can be charged to 4.2v but not all.18650 lfp battery cannot bear a charge of more than 3.65V and NMC 18650 can be charged to 4.2v. Therefore it is necessary to get information from the manufacturer.

.What happens if the 18650 battery voltage exceeds 4.2v?

Although the 18650 li-ion batteries are protected with auto shut to prevent overcharging or discharging.

Even so, if you use the battery in the wrong way to charge more than 4.2 volts, it may has safety hazard.

Make sure the specific charger is of good quality and is designed not to exceed the rated voltage. A poorly built battery can show uncertain results on overcharging it. So keep your batteries on notice when are being charged and do not let them exceed 4.2v.

.How to prevent the 18650 battery voltage from exceeding the normal range?

Your battery exceeds the spike of voltage, now it’s time to think about your battery safety.

When you are using 18650 rechargeable battery. a safety management system is required to ensure your battery’s safety which otherwise can get premature worn out.

This shield is provided with a cut-off system which saves the battery from exceeding the normal value of the voltage

.What factors affect the voltage of the 18650 battery?

The voltage is affected by some parameters:

  • The chemistry of the cell and chemical reactions involved in the battery system determines the voltage of the battery
  • The concentration of reactants in the battery increases the forward reactions which increase voltage but also cause voltage drop due to the rise of resistance.
  • The increased temperature also increases resistance in the circuit so voltage decreased. While the current increases with increased temperature.

The surface area of electrodes also matters in an increase of voltage.

How to Pick the Best 18650 Battery and 18650 Battery Charger

Lithium-ion 18650 batteries are a very popular choice for high-power devices that also require long-lasting batteries in terms of capacity, low self-discharge rate, and a large number of charging and discharging cycles.

18650 rechargeable batteries come in countless versions, with many features, some of the most important being capacity, maximum pulse and continuous drain current, charging current, protective electronics, etc.

Updated: November 12, 2021.

650 Battery Dimensions

As its name suggests, 18650 battery dimensions are (diameter x length) 18 × 65 mm (0.70866 x 2.5590 inches).

Actual dimensions slightly differ from manufacturer to manufacturer, but these small variations in size usually make no problems.

Before buying new 18650 batteries, there are few things to consider.

650 Battery Features and Specifications

Capacity and maximum discharge current. these two values are closely related since high capacity design limits maximum safe discharge rate and vice versa, high discharge current design limits the capacity of lithium batteries.

For example, high-capacity 18650 batteries have capacities up to and even more than 5000 mAh, but the maximum safe continuous discharge rate of such batteries is often in the 3-10 Amps range. high-capacity 18650 batteries.

On the other hand, 18650 batteries that are able to provide continuously 20-30 Amps and up to 40-50 Amps for 1-5 seconds safely, usually have a capacity in the 2500-3000 mAh range. high-drain 18650 batteries.

Note: when promoting their batteries, some manufacturers tend to overestimate the characteristics of their batteries. Thus, it is very important to read reviews and recommendations of other users as well, not just specifications and features provided by manufacturers. Or go for reputable brands and perhaps pay slightly more.

Flat or button positive (top) side. there are two versions of positive (top) side: flat top and button top.

Most of the devices support the use of both types, but just to be sure check the documentation of your device or go for the type that is already working well with your devices. better safe than sorry.

Soldering tabs or not. if you have issues with the 18650 battery pack, replace all the batteries with the new ones that have the capacity and charging/discharging currents in the same range (or better) as old batteries.

Always use the same batteries from the same manufacturer, preferably from the same batch and if you have to solder their tabs, let the professionals solder them for you since it can be a very tricky task to do. Or go for an OEM replacement battery pack, which can cost more, but it is a safer option if you are not absolutely sure what are you doing!

Protected 18650 batteries. since lithium-ion batteries are sensitive to charging and discharging conditions, their temperature, and other parameters, some 18650 models come with built-in protective electronics, which monitor the parameters of the battery and if required, protect the battery by shutting it off until conditions are changed.

Protective electronics require some space and thus slightly decrease the capacity of the batteries. IMHO, more than a worth feature, unless your device already has some sort of battery monitoring function.

Unprotected 18650 batteries feature a somewhat larger capacity, but their condition must be monitored by the external device.

Rewrapped batteries. some manufacturers buy cheap 18650 batteries, wrap them as their own and sell on the market, sometimes with highly exaggerated claims regarding their capacity and currents. On the other hand, reputable sellers like Panasonic, Samsung, LG, Sony, etc. thoroughly test their batteries and discard the bad ones. Of course, batteries from such brands cost more, but in the long run, their batteries are actually cheaper.

The following table lists few high quality 18650 batteries with their most common features:

Model Capacity Max. Continuous Current Comment
LG HD2 2000 mAh 30 A Strong, decent capacity
LG HE4 2500 mAh 20 A Nicely balanced battery
LG HB6 1500 mAh 30 A Very powerful battery
LG HG2 3000 mAh 20 A Strong and good capacity
Panasonic NCR18650B 3400 mAh 6.8 A (12 A, 5 sec) For low current devices
Samsung 25R 2500 mAh 20 A (30 A) GOLDEN STANDARD 🙂
Samsung 30Q 3000 mAh 15 A Can go up to 20A, but.
Sony VTC4 2100 mAh 30 A Strong, decent capacity
Sony VTC5 2600 mAh 20 A Nicely balanced battery

Note: Amazon affiliate links in the table open in the new Windows, feel free to check them.

Samsung INR18650-25R 18650 2500mAh Battery

Samsung INR18650-25R 18650 2500mAh or for short Samsung 25R is the golden standard regarding high power 18650 batteries. It has a high maximum continuous current of 20 Amps and many people have pushed it to its limits draining it with 30-40 or even more Amps (obviously, not recommended).

Its capacity of 2500 mAh at first looks modest, but if you take the higher capacity battery and drain it with 15-30 Amps, the actual capacity will be decreased, just like the number of charging and discharging cycles.

For low current devices, Panasonic NCR18650B features 3400 mAh capacity and it is able to provide almost 7 Amps (6.8 Amps, to be correct) safely.

Over time, manufacturers improve their designs and new batteries come with larger capacities and larger supported drain currents, but these batteries in the list have been tested in real-life applications countless times.

IMR, INR, IFR, or ICR 18650 Batteries

Labels of 18650 batteries often include abbreviations like IMR, INR, IFR, or ICR. These abbreviations describe actual battery chemistry:

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.

650 Battery Chargers

Modern 18650 battery chargers are intelligent battery chargers that can sense the battery type, chemistry, condition, etc.

Often these battery chargers can be used for charging a broad range of batteries, including NiCd, NiMH, and various lithium rechargeable batteries.

The most important features of intelligent battery chargers include:

When choosing a battery charger for your needs, pick a battery charger according to your current, but also future needs, too.

650 Batteries With USB Built-in Charger

To simplify the charging of 18650 batteries, some models feature a built-in USB battery charger. when charging is required, the battery is simply connected to a USB port, and onboard electronics monitor battery parameters and do all the work.

These models are highly recommended for people needing just a few 18650 batteries for their devices.

Although built-in USB battery chargers require some space and thus decrease the battery capacity, they also often monitor battery condition during operation and protect it, if required.

650 Battery Equivalents

When replacing the 18650 battery, the best option is to use another 18650 battery with the same, preferably better characteristics.

However, some devices allow the use of other batteries, like 3xAAA batteries, 2xCR123A batteries, and similar.

Also, the CR123A battery is available as a non-rechargeable lithium battery providing 3.0 V and as a rechargeable lithium-ion battery (often designated 17340, 17345, or 16340 battery) providing 3.6. 3.7 V.

This difference in voltage (3.6 vs 6 vs 7.2 volts) can damage many devices and one must check the documentation of a particular device to be absolutely sure if 2xCR123A batteries are supported.

Note: non-rechargeable lithium CR123A batteries from reputable brands have a shelf-life of often 10 or even more years and even after 10 years, they can provide large currents easily. Thus, CR123A batteries are often recommended for standby devices like EDC flashlights, panic lights, and similar devices that are often not used for years, but when they are used, they must operate reliably.

For devices that are often used, a rechargeable 18650 battery is recommended choice. But for standby applications, 3 high-quality AAA batteries (alkaline batteries, not rechargeable NiCd or NiMH batteries) are a more reliable choice.

Even if you have rechargeable NiCd or NiMH AAA batteries, do yourself a favor and get one good 18650 battery with a built-in USB charger. such a battery will easily outperform 3xAAA batteries and it can withstand more charging/discharging cycles.

650 Battery Flashlights

18650 batteries are commonly used as high-power and high-density energy sources for LED flashlights, ranging from compact EDC flashlights to strong and powerful tactical flashlights.

18650 flashlights usually feature one to two 18650 batteries, rarely more. only high-output, very bright flashlights feature three, four, or even more 18650 batteries.

Since LED flashlights use a built-in LED electronic management system, some 18650 LED flashlights allow the users to use either 18650 batteries, CR123A batteries, or AA batteries.

As said before, two CR123A batteries may replace a single 18650 battery, which is recommended for EDC flashlights that are rarely used but must operate reliably even after years of storage.

In order to provide the highest possible IPX waterproof and dustproof rating, some 18650 LED flashlights use various USB magnetic charging cables, allowing the batteries to be recharged without any openings on the battery’s body.

Amazon Search:

Note: Amazon link opens in the new window, feel free to check it for the most up-to-date offers and prices.

650 Battery vs 26650 Battery

18650 and 26650 batteries share the same length, but the 26650 battery is wider and has some ~2x larger volume.

Thus 26650 batteries are often used in devices requiring even more power and energy. 18650 battery packs plenty of energy, but 26650 packs on average 2x more.

18650 battery can be used instead of 26650 battery using a special battery holder, just be sure that 18650 battery can provide enough current for that particular device.

IMHO, 18650 batteries are great, but if your device supports the use of 26650 batteries, go for 26650 batteries.

650 Battery Frequently Asked Questions. 18650 Battery FAQ

Here are some of the most common questions about 18650 batteries:

How to charge a 18650 battery?

Depending on the 18650 battery type, the best way to charge the 18650 battery is to use a 18650 lithium-ion battery charger.

battery, technologies, 18650, lithium

18650 batteries that feature micro-USB or similar charging ports may be used via USB charging ports found on computers, laptops, or using USB wall chargers.

How long do 18650 batteries last?

18650 battery may last up to 300-500 charging cycles. after which its capacity drops down or below 80% of the nominal capacity.

How long does it take to charge a 18650 battery?

Charging time depends on the battery capacity and charging current, but it shouldn’t be too fast. charging times around 3-5 hours are considered optimal, although there are models that can be charged with much stronger currents.

18650 battery storage best practices?

18650 battery should be stored at room temperature (68-77°F, 20-25°C) in a dry, non-condensing area. Also, the lithium-ion batteries should be stored and transported in a semi-charged state (50-60% of nominal charge).

18650 battery should not be carried in the or bag with metal items (keys, for example) present which may short-circuit the battery.

battery, technologies, 18650, lithium

What is the voltage of a completely charged 18650 battery?

End charging voltage depends on the exact battery chemistry and ranges from 3.6 to 4.2 volts.

Is a 18650 battery the same as AA?

No, the 18650 battery is a lithium rechargeable cylindrical battery featuring physical dimensions of 18.6 × 65.2 mm, while the AA batteries feature physical dimensions of 14.5 x 50.5 mm and are available in various both non-rechargeable and rechargeable chemistries.

Some devices intended for 18650 batteries also come with a special battery holder that allows them to use either 18650 or AA batteries, but due to the larger dimensions, 18650 batteries are able to store more energy than AA batteries.

Which is better, a single 18650 battery or 3x AAA batteries?

AAA batteries feature physical dimensions of 10.5 x 44.5 mm, while 18650 batteries feature physical dimensions of 18.6 x 65.2 mm.

Some devices intended for 18650 batteries come with special battery holders allowing them to use either 18650 batteries or 3x AAA batteries instead of a single 18650 battery.

Although such battery holders allow the user to use whatever battery is available, a single 18650 battery is able to store more energy than three AAA batteries.

Is there any reason you shouldn’t or can’t make a vehicle battery out of several lithium 18650 batteries?

While 18650 batteries may be used for making large battery packs, each of these 18650 batteries must have a separate wire for monitoring the battery’s condition and for equalizing the battery.

Since such battery packs require a huge number of individual 18650 battery cells, such battery packs would also require a rather complex Battery Management System (BMS).

For example, in order to create a 12V 100Ah battery pack using 3.2V 3000 mAh 18650 Lithium Iron Phosphate (LiFePO4) batteries, one would need 136 (4S34P) 18650 batteries, and only 4 (four) 3.2V 100Ah Lithium Iron Phosphate (LiFePO4) battery cells.

It is much easier and less complex to connect 4 cells in series than 136 batteries in 4S34P configuration.

And electric vehicles use much larger battery packs than simple 12V 100Ah batteries.

For short: the best battery replacement for a 18650 battery is another 18650 battery. plain and simple. When choosing new batteries, consider your old batteries and the device(s) you have, and their requirements.

Note: never, but really never charge lithium batteries with chargers not designed for such batteries. Also, never throw them in fire, leave them in the hot car, or similar. And, after they served you well, dispose of them properly (they can be almost 100% recycled!).

Leave a Comment