18650 Battery length. Can you overcharge 18650 batteries?

650 Battery FAQ

18650 li-ion cells are cylindrical rechargeable cells, shaped like giant AA alkaline batteries. They have a higher nominal discharge voltage of 3.7V, which gives them a signifcant power advantage over the older alkaline(1.5V) and nimh/nicad(1.2V) chemistries. 18650 li-ion cells can be found in laptops, power tool battery packs, electric cars and countless consumer goods.

The term 18650 comes from the IEC naming scheme for round cells based on their physical dimensions. The first two digits are its diameter in millimeters, while the last 3 digits are for its height in 1/10th millimeters. Based on this naming convention, the original 18650 cells would be 18mm in diameter x 65.0mm in length.

What does PCB protected mean?

Most modern raw lithium-ion cells contain passive safety features like PTC (pressure, temperature and current) protection, however the cells may still be damaged if they are over-charged or over-discharged. To reduce the risk of damage, battery manufacturers will add a tiny circuit board (PCB) to the bottom of the raw cell to monitor its voltage and disconnect power if it senses an error. The protection PCB usually adds 2-3mm to the length of the cell, and the small metal Band connecting the PCB to the positive terminal will add a ~0.5mm bulge to its diameter.

Button top cells have a positive terminal that protrudes 1-2mm (ie, the button), similar to the positive terminal on AA batteries. The button allows the cells to be stacked in series in a flashlight or similar consumer device. In contrast the positive terminal on a flat-top cell does not protrude, and are intended to be tack-welded into a larger battery pack. If a flat-top cell is used in a device that only accepts button-top cells, the flat-top might not form a reliable electrical connection.

Are 3400mAh cells worth the added cost over 2600mAh cells?

No, it is not safe to mix li-ion cells with different cell capacities or charge levels. Doing so may cause some cells to discharge below their lower safety limit and causing permanent cell damage. Always use cells of matching capacity and charge level.

As you may have already noticed, the 18650 specification has become more of a suggestion than a standard. The cell lengths seem to increase every year. Panasonic’s popular NCR18650 raw cells are already larger than the specification, and the addition of a protection PCB virtually guarantees all cells will greatly exceed the original 18mm x 65mm specification. We have found that 1/3 of cell models exceed even their own manufacturer’s size specifications, so their dimensions should be used only as a starting point.

In order to help our customers narrow down what cells to use, we have compiled a list of measurements below. Please bear in mind that the measurements are based on a limited number of test cells at the time, and that battery manufacturers may change their suppliers and specifications at any time. If you are unsure if a particular cell will fit or discover our measurements are out of date, please contact our tech support department for assistance.

Please DO NOT use metal tools when measuring batteries. A short circuit could result in damage to the battery, fire or bodily injury. Most PCB protected cells usually have a metal Band running the length of the cell, and are slightly longer on one side. Take multiple measurements at different points around the circumference and use the largest value.

LED2 / LED8. The LED2 and LED8 may be used with either flat-top or button-top PCB protected 18650 li-ion cells up to 18.8mm diameter x 69mm overall length, and 68mm max body length. If the door is difficult to close or the latch does not snap back into locking position, the cells are probably the wrong size. DO NOT use excessive force! The battery door should require less than 4.5lb/2kg of force to close.

RADIUM. The RADIUM LED may be used with button-top PCB protected 18650 cells up to 19mm diameter x 70mm overall length. The button should protrude at least 0.5mm to maintain proper electrical contact. If the cell has a button shorter than 0.5mm, the product may lose power or reset randomly. If this happens try a cell with a more pronounced button, or rotate the cells until the edge with the metal Band is facing the battery door.

18650, battery, length, overcharge, batteries

650 battery length

The 18650 battery is a model of rechargeable battery of lithium of 3.7 volts. These rechargeable batteries are very similar to AA batteries but a little bit bigger size. These 18650 batteries also calling Li-ion batteries.

The advantage of these rechargeable batteries is there are very lightweight batteries. Furthermore, have high energy capacity and resistance to discharge. In addition, those can resist many charging cycles.

Where can you use 18650 batteries?

Y ou can use this kind of 18650 batteries in many electronical devices. From the little ones could be flashlights, lights for bikes to powerful devices such as, drills, electrical cars, electrical bikes, lawnmowers. Also is possible to build battery packs to use for a drone motor, electrical bike, among others.

When we refer about capacity this one is express in milliamps/hour this indicated us the autonomy of each 18650 battery, being of longer duration the more mAh has these 18650 batteries. The most common capacity of rechargeable batteries is between 2000 mAh and 4000 mAh.

When we refer about discharge this one is express in amperes this is the maximum current that can supply the power demand of the device. The capacity of the rechargeable batteries could range from one to others, from 3 A (amps) to 35 A (amps).

What is the meaning of 18650

Many people ask to us what the meaning is of 18650. The 18 indicates the diameter (18 mm) of 18650 battery in millimeters. Next, the number 65 indicates its length (65 mm). The total length of the 18650 battery with the head and protections.

How to choose the best 18650 battery for your device

  • Firstly, you must know the power of the device you need to power and the maximum length that the rechargeable battery should be to fits inside the device.
  • The power of the device that might be indicated in amps should be stay below of the battery discharge (amps) you use, or you will never get it to
  • You must be conscious that the intensity is always defined by the needs of the device until the maximum that the 18650 batteries resists. This means that the rechargeable battery with the higher discharge rates can be use in devices with lower power and the autonomy will be greater than that shown in the specifications.
  • For example, if you have a flashlight what consume 12 amps, that will be the maximum intensity of work reach out although the 18650 battery has 30 amps or more.

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650 battery life cycle

All batteries have a limited life cycle. If you’re unfamiliar with the term “life cycle,” it refers to the number of times a battery is fully charged and entirely discharged until it can only supply 80% or less of its original capacity. 18650 batteries are constructed of lithium-ion and have a life cycle of 300 to 500 cycles. over, If the maximum discharge current limit (A) is exceeded, the cycle life can be reduced to as few as 50 cycles. In case you are a battery hog, have no fear since proper usage can extend the battery life cycle. T he exact number of cycles can vary quite a bit, depending on how the battery is used and charged. Some high-quality 18650 batteries might exceed the 500-cycle mark when treated optimally.

Charging habits

Whether it’s a phone battery or a cylindrical battery, when it comes to lithium-ion batteries, you must adhere to a set of rules to guarantee that you may use them happily for an extended period of time. These guidelines include proper charging and discharging practices. The charging habit involves not entirely charging and draining the battery, in addition to adhering to a range of other guidelines.

  • The guideline advises that batteries should not be charged over 80% and should not be discharged below 20% since this can decrease their life and cause them to wear out more quickly. With this method, you will use the battery for a shorter time and charge it more frequently, but you will get more than 300 to 500 life cycles out of it. Furthermore, the idea behind this approach is that it gives the battery room to breathe, preventing any buildup of pressure. While this approach can potentially prolong the overall lifespan of a battery, it might not always be practical in all usage scenarios.
  • Charge the battery before using it. If you are not going to use the battery for a while, avoid charging and storing it because this puts the battery under stress. Besides, the likelihood of any dangers associated with storing batteries decreases.


While using the Rapid charging technology is pleasant, it has the potential to reduce battery life. This technology is capable of charging at a rate of up to 4A, whereas standard chargers run at a rate of 1.0A-1.5A. Just as rapidly depleting the battery degrades its life, Rapid charging also negatively affects battery life. Additionally, Rapid charging produces heat, which is terrible for the battery. Also, after charging, the battery should be cooled to room temperature before use.

It’s also worth noting that many modern devices and chargers have intelligent systems to manage heat and charging speed to minimize these downsides.

Make sure that the charger features a set of safe charge protection such as overcharging. Ascertain that the charger includes a set of charge safety features, such as overcharging protection. This safeguard is designed to prevent charging when the battery is near to being fully charged; it significantly contributes to the battery’s lifespan extension.


The temperature has a significant effect on the performance of a battery. When the environment is extremely cold or extremely hot, the battery cannot operate optimally. Heat can accelerate the degradation of nearly every battery component and cause safety risks, such as fire or explosions. The ideal environment temperature for optimal performance and longevity is room temperature (around 60°F to 77°F or 20°C to 25°C).

How long do 18650 batteries take to charge?

The time required to charge 18650 batteries is dependent on the battery’s capacity, the charger, and a few other factors. Charging a 18650 battery takes around 4 hours with a standard charger, but just 3 hours or less with a charger equipped with Rapid-charge technology.

In detail, batteries with a larger capacity (mAh) have long, thin electrodes, while batteries with a lower capacity (mAh) have shorter, thicker electrodes. Because low-capacity cells have a lower internal resistance, they can be charged and discharged more quickly.

Also, the ambient temperature plays a significant role. It is recommended to charge the battery at temperatures greater than 0°C and less than 45°C. Not only will the battery charge normally at this temperature range, but it is also safe for the battery, as the battery can catch fire or explode at higher temperatures.

18650, battery, length, overcharge, batteries

How often should you change your 18650 batteries?

18650 lithium batteries have a life expectancy of 300 to 500 cycles. As a result, you can replace them when they reach the end of their life cycle. You’ll notice the battery getting close to the end of its life cycle when it starts to hold less and less charge. This usually happens in time and initially, it will not be that noticeable, however after a certain number of charge/discharge cycles you can see the battery not being able to hold as much charge as it used to.

Generally speaking, manufacturers incorporate integrated circuits that provide multi-charging safety features like overcharge protection. When the battery is close to being fully charged, this integrated circuit interrupts the charging process. However, it is wise to keep an eye on the battery whenever you are charging it because batteries are complex, and anything is possible.

It’s worth mentioning that 18650 batteries come in two types: protected and unprotected. The protected 18650 batteries feature the integrated circuit discussed previously, while the unprotected ones do not. Due to the absence of this technology, unprotected batteries are less expensive, but there is a risk of overcharging and other battery-related threats. As a result, it is recommended that you purchase protected 18650 batteries.

Protected vs Unprotected 18650 Battery

Most 18650 batteries will come in either a protected or unprotected type.

The main difference between the two is that the protected class has a circuit board that prevents the battery from overcharging, over-discharging, and short-circuiting.

The unprotected type does not have this circuit board, which means it is more susceptible to these issues. However, the unprotected type is usually cheaper and has a higher capacity.

On the other hand, Protected 18650 batteries are a bit more expensive but offer better safety for the user.

Applications, How They’re Used?

18650 batteries are most commonly used in electronic cigarettes, flashlights, and other electronics due to their high capacity and reliability.

In electronic cigarettes, the battery is used to heat the coil, producing vapour. Most electronic cigarettes will use one or two 18650 batteries.

In flashlights, the battery is used to power the LED light.

18650 batteries are also used in other devices, such as electric scooters, solar panels, medical equipment, toys, and remote control cars. They are also used in almost all portable and cordless power tools.

Battery Cycle Of Lithium-Ion 18650

The 18650 battery has a standard cycle of lithium-ion, which is 300-500. This means that it can be recharged and used again up to 500 times before it needs to be replaced.

This makes the 18650 battery a very economical choice for those who use electronic devices regularly and need to recharge their batteries often.

Compared with several other battery types like AA, AAA, and CR123, 18650 is considered the better one for those who need a reliable and affordable battery for their electronic devices.

The battery also has a voltage of 3.7V, making it compatible with most electronic devices.

What Are The Benefits of A 18650 Battery?

The 18650 battery is powerful and durable for high-end flashlights and other portable lighting products. Here are several benefits over other types of batteries:

  • Longer lasting power: An 18650 battery can last up to 500 charge cycles, significantly longer than most other types of batteries.
  • powerful: store more energy than other batteries, making it ideal for devices that require a lot of power.
  • environmentally friendly: 18650 batteries are built with lithium, a more environmentally friendly material than the lead used in other types of batteries.
  • Rechargeable: An 18650 battery can be recharged multiple times, making it more sustainable than disposable batteries.
  • Versatile: 18650 batteries can be used in various devices.

Ⅱ Uses of 18650 Lithium battery

The 18650 battery life theory is 1000 cycles of charging. Because of the large capacity per unit density, most of them are used in laptop batteries. In addition, because the 18650 has very good stability at work, it is widely used in various electronic fields: often used in high-end glare flashlights and portable power supply, wireless data transmitter, electric heating warm clothes, shoes, portable instruments, portable lighting equipment, portable printers, industrial instruments, medical instruments, etc.

The working principle of a lithium-ion battery refers to its charging and discharging principle. When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The carbon as the negative electrode has a layered structure. It has many micropores. The lithium ions that reach the negative electrode are embedded in the micropores of the carbon layer. The more lithium ions are inserted, the higher the charging capacity.

In the same way, when the battery is discharged (that is, the process when we use the battery), the lithium ions embedded in the carbon layer of the negative electrode are released and move back to the positive electrode. The more lithium ions that return to the positive electrode, the higher the discharge capacity. What we usually call battery capacity refers to the discharge capacity.

It is not difficult to see that during the charging and discharging process of lithium-ion batteries, lithium ions are in a state of movement from positive → negative → positive. If we compare the lithium-ion battery to a rocking chair, the two ends of the rocking chair are the two poles of the battery, and the lithium ion is like an excellent athlete running back and forth on both ends of the rocking chair.

Charging and discharging process

Lithium battery charging control is divided into two stages. The first stage is constant current charging. When the battery voltage is lower than 4.2V, the charger will charge with a constant current. The second stage is the constant voltage charging stage. When the battery voltage reaches 4.2V, due to the characteristics of lithium batteries, if the voltage is higher, it will be damaged. The charger will fix the voltage at 4.2V and the charging current will gradually decrease. When it is reduced to a certain value (generally 1/10 of the set current), the charging circuit is cut off, the charging completion indicator light is on, and the charging is completed.

Excessive charging and discharging of lithium-ion batteries can cause permanent damage to the positive and negative electrodes. The excessive discharge causes the negative carbon sheet structure to collapse, and the collapse will cause the lithium ions to be unable to be inserted during the charging process; overcharging causes too many lithium ions to be inserted into the negative carbon structure, causing some of the lithium ions to be unable to be released anymore.

Some chargers are implemented using cheap solutions, and the control accuracy is not good enough, which can easily cause abnormal battery charging and even damage the battery. When choosing a charger, try to choose a big brand of 18650 lithium-ion battery charger. The brand-guaranteed 18650 lithium-ion battery charger has four protections: short-circuit protection, over-current protection, over-voltage protection, battery reverse connection protection, etc.

Overcharge protection: When the charger overcharges the lithium-ion battery, in order to prevent the internal pressure from rising due to temperature rise, the charging state must be terminated. For this reason, the protection device needs to monitor the battery voltage, and when it reaches the battery overcharge voltage, it activates the overcharge protection function and stops charging.

Over-discharge protection: To prevent the over-discharge of the lithium-ion battery, when the voltage of the lithium-ion battery is lower than its over-discharge voltage detection point, the over-discharge protection is activated, the discharge is stopped, and the battery is kept in a low quiescent current standby mode.

18650, battery, length, overcharge, batteries

Over-current and short-circuit protection: When the discharge current of the lithium-ion battery is too large or a short-circuit condition occurs, the protection device will activate the over-current protection function.

Ⅳ General configuration

The nominal voltage of a single cell is generally: 3.6V or 3.7V

The charging voltage is generally: 4.20V (4.2V-4.3V for lithium cobalt oxide)

The minimum discharge termination voltage is generally: 2.75V, lower than this voltage will easily lead to a serious drop in battery capacity or even scrap

Maximum charge termination voltage: 4.20V

Capacity: above 1000mAh, the conventional capacity is 2200mAh-3200mAh, the 18650 battery capacity is the highest is LG, which can achieve 3600mAh, but the price is not low.

Ⅴ Advantages and Disadvantages


Large capacity. The capacity of 18650 lithium battery is generally between 1200mah and 3600mah, while the general battery capacity is only about 800mah. If combined into a 18650 lithium battery pack, the 18650 lithium battery pack can easily exceed 5000mah.

Long life. The 18650 lithium battery has a long life, and the cycle life can reach more than 500 times in normal use, which is more than twice that of ordinary batteries.

High safety performance. The 18650 lithium battery has high safety performance. In order to prevent the battery from short-circuiting, the positive and negative electrodes of the 18650 lithium battery are separated. Therefore, the short-circuit phenomenon may have been reduced to the extreme. A protection board can be installed to avoid overcharge and over-discharge of the battery, which can also extend the service life of the battery.

High voltage. The voltage of the 18650 lithium battery is generally 3.6V, 3.8V, and 4.2V, which is much higher than the 1.2V voltage of nickel-cadmium and nickel-metal hydride batteries.

No memory effect, It is not necessary to empty the remaining power before charging, which is convenient to use.

Small internal resistance: The internal resistance of polymer batteries is smaller than that of ordinary liquid batteries. The internal resistance of polymer batteries can even be below 35mΩ, which greatly reduces the self-consumption of the battery and prolongs the standby time of the mobile phone. This kind of polymer lithium battery that supports a large discharge current is an ideal choice for remote control models, and it has become the most promising product to replace Ni-MH batteries.

It can be combined in series or parallel to form a 18650 lithium battery pack.

Wide range of use: Notebook computers, walkie-talkies, portable DVDs, instrumentation, audio equipment, model airplanes, toys, camcorders, digital cameras, and other electronic equipment.


The biggest disadvantage of the 18650 lithium battery is that its size has been fixed, and it is not well-positioned when installed in some notebooks or some products. Of course, this disadvantage can also be said to be an advantage. This is compared with other lithium batteries such as polymer lithium batteries. This is a disadvantage in terms of customizable and transformable size. Compared to some products with specified battery specifications, it has become an advantage.

The production of 18650 lithium batteries requires a protection circuit to prevent the battery from being overcharged and causing discharge. Of course, this is necessary for lithium batteries, which is also a common disadvantage of lithium batteries, because the materials used in lithium batteries are basically lithium cobalt oxide materials, and lithium cobalt oxide materials cannot discharge at high currents.

The 18650 lithium battery requires high production conditions. Compared with the general battery production, the 18650 lithium battery requires high production conditions, which undoubtedly increases the production cost.

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