What current charges the li-ion 18650 and how to use the battery correctly? How can such a power source extend its service life? These questions arise in a wide variety of electronics industries. A lithium-ion battery is a type of electric current battery. In 1991, SONY launched the battery into the market, and it immediately began to be widely used in household and electronic appliances.
These batteries serve as power sources for mobile phones, laptops and video cameras, electronic cigarettes and electric vehicles. All modern lithium-ion batteries prevent overheating and overcharging. However, the problem of charge loss at low temperatures has not disappeared.
Among the undeniable advantages of lithium-ion batteries, we would like to highlight the following:
- good capacity;
- low self-discharge;
- no maintenance required.
Original chargers
A lithium-ion battery charger is quite similar to a lead-acid battery charger. They differ only in that the lithium-ion power source has a very high voltage on each bank and strict tolerance requirements for it.
If for lead-acid batteries some inaccuracies in the boundary voltages during charging can be tolerated, then with lithium-ion cells everything is completely different. When the voltage increases to 4.2 V during charging, the voltage supply must be stopped.
It is allowed to exceed only 0.05 V. The most ideal charger for lithium-ion batteries is a voltage stabilizer. Lithium must be charged at a stable voltage with a current limit at the beginning of the charge. It is very important. Charging will be considered complete if, with a stable charge of 4.2 V, there is no current or it has a very small value of about 5-7 mA.
Electrical circuit for charging an 18650 cell
On top of that, when you install the stabilizer on the radiator, you can safely recharge your batteries without fear that the charger will overheat and then catch fire. This can happen with Chinese chargers. The operation of the circuit is quite simple. First, the battery is charged with a constant current determined by the resistance of resistor R4.
When the battery has a voltage of 4.2 V, the direct current will begin to charge it. When it drops to the lowest values, the LED in the circuit will stop lighting. Recommended currents for charging lithium-ion batteries should not exceed 10% of the volume of the battery itself in order to increase the life of your power source. With a resistor R4 value of 11 Ohms, the current in the circuit will be 100 mA. If a 5 ohm resistance is used, the charging current will be 230 mA.
How to extend the life of your 18650
If you are leaving a lithium-ion battery unused for a period of time, we recommend storing the battery separately from the device it powers. A fully charged cell will lose some of its charge after some time. If the battery has a very low charge or is completely discharged, it can permanently fail after a long period of hibernation. It is optimal to store the 18650 at a charge level of 50%.
Do not allow the battery to be completely discharged or recharged. Lithium-ion batteries do not have a memory effect. Such batteries are charged only when the charge is completely exhausted. This will also extend the life of the battery.
Lithium ions do not like heat or cold. Optimal temperatures for the battery range from 10 to 25 degrees. Cold will not only reduce operating time, but will also destroy the chemical system of the battery. Probably everyone has noticed how the charge level on your phone instantly drops in cold weather.
If you are going to charge a lithium-ion battery with a charger from a store, make sure that it is not Chinese. Very often they are assembled from cheap materials and not always using the correct technology.
This, in turn, can lead to a fire. When using such batteries, always follow the operating and storage instructions to avoid the possibility of an explosion due to overheating or complete failure. This will extend the life of the lithium-ion battery and save you from unnecessary costs.
Take care of your battery! She is your assistant.
The li ion 18650 battery is a cylindrical battery. It is not much different from ordinary AA “finger” batteries, but they are larger in size. They are 66 mm long and 18 mm in diameter.
Contents
Types and types of Li Ion 18650 batteries
All 18650 batteries can be divided into types based on cathode material. The main operational characteristics of batteries depend on this component: capacity and possible discharge current.
The most common are lithium-cobalt batteries. They differ from other batteries in their large capacity. Therefore, they can be used longer.
There is also a group of lithium-manganese batteries. Compared to lithium-cobalt batteries, they have a lower capacity, but at the same time have a higher discharge current.
The last group is lithium ferrophosphate batteries. Although they do not have a large capacity or high voltage, they can be operated for more than 1000 cycles. In addition, until fully charged, you need to keep the batteries in the station for 1 hour.
18650 batteries with protection
Safety requirements for the operation of lithium-ion batteries state that the voltage inside the batteries must be in the range of 2.5-4.2 volts. It is very difficult to control this parameter on your own, so a board with protection was invented specifically for this. This element prevents the voltage from going beyond the specified range.
Manufacturers solder this board to the pins using steel or aluminum tape. Large nutrient factories rarely produce such protections. The devices for which they are manufactured have charge-discharge controllers. These are batteries for laptops, screwdrivers and other complex units.
Most of the protected 18650 lithium-ion batteries are produced by Chinese manufacturers. A protective board is soldered onto an unprotected battery and wrapped in a special thermal protective material. Their length, due to the use of the board, increases by several millimeters.
It is better to equip all devices that do not have an element for monitoring the battery status with protected batteries. Otherwise, they may fail, discharge to zero or explode. In this case, the protection will not be able to prevent the battery from overheating. It controls the state of tension.
How the marking is deciphered
As an example, consider the ICR18650-26F M lithium-ion battery.
- The first symbol “I” is used on all elements of this type that are created using the same technology;
- The second letter allows you to understand what material the cathode is made of. For lithium-ion batteries, this can be cobalt - C, manganese - M, iron phosphate - F;
- The next letter – R – stands for battery;
- The 18650 numbers can be divided into two blocks: 18 and 65. These are the length and diameter, respectively;
- The last digit 0 is the shape, that is, the cylinder.
At the same time, the markings of different manufacturers may vary greatly.
Where are 18650 batteries used?
The scope of batteries and the frequency of their use is much wider than many people think. Due to the fact that they are closed with special protection, they are not always visible.
Installed in the following devices:
- Laptops;
- Flashlights;
- Power Bank;
- Various gadgets.
They are used wherever ordinary AA batteries are unable to cope with the task. Li ion 18650 batteries have a higher capacity and voltage, they can be recharged and reused many times.
How to determine plus and minus
Compared to AA and AAA batteries, lithium-ion batteries do not have such a noticeable external difference between the positive and negative terminals, but it’s quite easy to understand:
- On the “plus” side there are 3-4 small holes.
- The “plus” side sticks out a little.”
- “The minus is completely flat.
General characteristics of 18650
| Capacity (mAh) | Output voltage (V) | Maximum current (A) | Protection board |
|---|---|---|---|
| 1100 | 3.3 | +/- | |
| 1300 | 3.6 | 18 | +/- |
| 1620 | 3,6-3,7 | 20 | +/- |
| 2000 | 3,6-3,7 | 20-30 | +/- |
| 2100 | 3,6-3,7 | 20-30 | +/- |
| 2200 | 3,6-3,7 | 20-30 | +/- |
| 2400 | 3,6-3,7 | 20-30 | +/- |
| 2500 | 3,6-3,7 | 20-35 | +/- |
| 2600 | 3,6-3,7 | 20-35 | +/- |
| 2800 | 3,6-3,7 | 20-35 | +/- |
| 3000 | 3,6-3,7 | 20-35 | +/- |
| 3100 | 3,6-3,7 | 20-35 | +/- |
| 3200 | 3,6-3,7 | 20-35 | +/- |
| 3350 | 3,6-3,7 | 20-35 | +/- |
| 3400 | 3,6-3,7 | 20-35 | +/- |
| 3500 | 3,6-3,7 | 20-35 | +/- |
| 3600 | 3,6-3,7 | 20-35 | +/- |
The table shows the most popular batteries.
Dimensions with protection: 66.5*18 mm and 66*18 mm without protection. Weight on average about 40 grams.
Main manufacturers: Samsung, Fenix, Avant, LG, Panasonic, Olight, Camelion, Proconnect, Rombica, SANYO and SONY.
How to choose the right 18650 battery for yourself
Lithium-ion batteries differ from each other in several characteristics. Because of this, it is necessary to pay attention to their type and technical characteristics before making a purchase.
When choosing a li ion 18650 battery, you need to pay attention to the following characteristics:
- Energy intensity;
- Rated current;
- Voltage
- Tendency to overheat.
If you need to purchase batteries with greater autonomy, then you need to pay attention to the capacity, which is measured in mAh. But, the higher the capacitance indicator, the lower the current will be. Therefore, by sacrificing one, you can gain another. In simple terms, the current strength affects the tendency of the battery to overheat.
The battery voltage depends on the charge. Voltage can be nominal, minimum, maximum and real. The manufacturer indicates the initial voltage on the packaging. It is important that its value does not fall below 2.4 Volts, otherwise the battery will be extremely difficult to revive. If you use batteries that do not withstand high temperatures well, you may experience an explosion.
Battery connection diagrams
You can purchase cases for batteries, with the help of which several elements are combined into one large one. If you connect several of these batteries using cases in parallel, the capacity will increase by as much as the number of batteries that are connected 3600*3=10800 mAh. In this case, the voltage will be equal to the voltage of one battery. The duration of their use depends on the capacity.
Parallel connection of 18650 batteries They can be connected in series. In this case, the voltage will add up, and the capacity will remain equal to one battery. This can be done using a special case. By connecting 3 3.7 V batteries we get an 11.1 volt 3600 mAh battery.
Series connection of 18650 batteries How to check battery capacity
There are several effective ways to find out the capacity of any battery. Some of them do not require special expenses or special equipment, but only simple mathematical calculations.
The accuracy of such methods is not as high as when using special devices, but they allow you to find out the approximate capacity. For many this will be enough.
So, to calculate the capacitance using the free method, you need to use a known current. The battery specifications contain information about the current. A battery with a capacity of 3600 is charged for 36 hours with a current of 100 mAh. This means that the final result is obtained by multiplying two components: time and current. Therefore, knowing how much is required for a full charge, you can find out the capacity.
To measure capacity in another way, you will need to spend money. There are many smart chargers that can quickly measure capacity. They can be purchased at a specialty store or on aliexpress. They are used to measure various indicators, not just capacity.
A device that measures real capacitance To implement the third method, you will need such parts as a battery, a watch, an ammeter with a flashlight. You need to insert the battery into the flashlight and turn it on at maximum power. An ammeter is needed to measure current. If the flashlight shines for 20 hours with a current consumption of 100 mA, then we get 20 * 100 = 2000 mAh.
How to charge and with what current
Lithium-ion cells can be charged at various stations. The main thing is that the voltage value is 5 V, and the current is from 0.5 to 1 of the nominal battery capacity. The lithium cell, which has a capacity of 2600 mAh, is charged with a current of 1.3 to 2.6 amperes.
The entire charging period can be divided into several stages. First, the unit, using a current of 0.2 of the capacity, charges for an hour. In this case, the voltage value varies between 4.1-4.2 volts. Then the tension increases.
In order not to bother yourself, you should just buy a charger for AA batteries.
How to restore a 18650 battery
An 18650 battery can only be restored if it is not completely discharged. Sometimes it is difficult to revive a battery that is not completely discharged. But there is one far from well-known option with disabling the board.
It is done like this:
- The protection in the form of a board is removed.
- The tester measures the voltage at the outputs. Its value should be in the range 2 -2.5 V.
- Using a charger with current regulation, you need to connect it to the battery, setting it to 100 mA and 4.2V.
If the battery starts charging, it means it is still alive and can be restored.
Detailed description of 18650 lithium-ion batteries, making a charging device with your own hands, nuances of application.
TEST:
To see if you have enough information about your lithium-ion battery:- What was the main disadvantage of the first 18650 battery models?
a) They exploded due to lithium metal inside - with frequent charging, accumulations appeared on the element, leading to an explosion.
b) The battery was too bulky and inconvenient.
- What problem have the manufacturers of modern 18650 models not yet gotten rid of?
a) The battery often overheats.
b) The battery quickly loses charge when exposed to negative temperatures.
- In what temperature range is it desirable to store the battery?
a) + 10 – + 25 – ideal indicators. The battery does not tolerate extremely cold or hot rooms.
b) Store the battery at low temperatures when not in use.
c) At a temperature of +30-45 degrees.
- Why can't I buy a charger made in China?
a) The case is too unreliable.
b) Low quality parts, correct assembly technology is not always followed.
- At what charge level is it advisable to store the battery?
a) The 18650 should be stored at a charge level that does not fall below 50%. A complete discharge cannot be performed.
b) Not lower than 10%.
Answers:
- a) The main disadvantage of the first models is the risk of explosion. Lithium metal grew overgrown with frequent charging and a short circuit occurred, leading to an explosion of the battery.
- b) Modern batteries do not tolerate low temperatures well - the charge drops very quickly.
- a) + 10 – + 25 – ideal indicators. Do not place the battery in other conditions.
- b) Chinese manufacturers often use low-quality parts when assembling devices, so they fail. The correct assembly technology is not always followed.
- a) If you plan to keep the battery idle for a long time, then make sure that the charge on it does not fall below 50%, otherwise the battery will deteriorate.
Owners of lithium-ion batteries The 18650 faces the question of what current to charge it with. Difficulties also arise in correct operation; people do not know exactly what such batteries are afraid of, or how to increase their operating time.
To assemble an electronic cigarette or flashlight yourself, you must study all aspects work with lithium-ion power supply.
Definition: Li-ion battery is an electric current battery that has become widespread among consumer electronics since 1991. It was this year that Sony Corporation presented the product to the wider market.
Answers to 5 Frequently Asked Questions
- What are lithium-ion batteries used for?
- As a power source. Such batteries are often used for various mobile phones, video cameras, laptops, for recharging electric vehicles or modern electronic cigarettes.
- Do the models have any disadvantages?
— The main drawback of the model was that the first developments literally exploded. This is explained by the fact that manufacturers placed an anode consisting of lithium metal inside. When a large number of charges and discharges occur, formations appear on the anode, leading to the short circuit of the electrodes. As a result, a fire occurs, and then an explosion. This problem has now been resolved.
- How was the problem with explosions solved?
— To make the structure safer, scientists replaced the core with graphite, and got rid of the problem with explosions. But there were still difficulties with the cathode caused by the cobalt oxide design. If the operational characteristics were violated, the explosions were repeated. That is why it was necessary to ensure that the device was not overcharged. It was extremely inconvenient for users to constantly monitor the charge level and the developers had to modify the device again. Modern models are safe. When developers began using lithium ferrophosphate batteries, they managed to get rid of this problem. Modern devices are manufactured in such a way that overcharging and overheating are impossible.
- Do modern models have disadvantages?
— The charge is lost if the battery is exposed to low temperatures.
- If you don't use the battery for a long time, will it deteriorate?
– If you do not lower the rarefaction level below 50%, it will not deteriorate.
3 benefits of battery
Lithium-ion batteries have a number of positive aspects, which is why they gained popularity:
- Extra large capacity battery
- Small self-discharge
- No special maintenance required.
Charging – 5 nuances
Charger Look at the picture of the original charger device. The charger designed for lithium-ion batteries is very similar to the lead-acid type of battery. The difference is that lithium-ion battery There are high voltages on each bank and severe voltage tolerance requirements.
This is interesting! The battery is called a “can” because of its similarity to the aluminum cans used for soft drinks.
"Banks" Most Popular Items nutrition with this form - 18650. The battery received this name because of its dimensions: diameter - 18 mm, height - 65 mm. When charging lead-acid batteries batteries, Minor inaccuracies in voltage indications are allowed. But with lithium-ion devices, everything is much more specific. When it happens charger, and the voltage increases to 4.2 Volts, the voltage to the element must be stopped immediately. The error is only 0.5 Volts.
Chinese exercise There are a large number of Chinese chargers designed for batteries of different materials. Without compromising performance, ion batteries are charged with a current of 0.8 A. But the voltage in the bank will have to be very strictly controlled. When the value is 4.2 Volts, immediately stop charging. But in the event that it is built into the jar controller, then you don’t have to worry about it, because the device will do everything on its own.
Chargers 4.2 Volt
As charger For a lithium-ion battery, a voltage stabilizer is used, limiting the current at the very beginning of charging. It is necessary to use an extremely stable voltage and limit the current at the very beginning of the charging process. Charging should be completed at the moment when the stable voltage is 4.2 Volts, absent current, or its value is very small - around 5-7 mA.
Oxidation When a battery rod is placed in graphite, then the voltage should not exceed 4.1 V per element. If this rule is neglected, the energy density will increase greatly and oxidation processes of the device will begin. As a result, the battery will fail. To avoid oxidation, modern models are equipped with additives - graphite in its pure form there is no inside. But similar models can still be found by chance.
How to properly charge Li-ion batteries. Parallel connection of batteries.
Homemade charger at home (with your own hands) - 1 circuit
For charging 18650 purchase a universal charger and constantly use a multimeter to find out the necessary parameters. But such a device is quite expensive. Minimum price – 2700 rubles.
Instead, you can spend just a few hours and assemble a charger device on one's own. The advantages of this assembly are low cost, reliability, and automatic battery shutdown. All the parts used for assembly can be found in any radio amateur's garage. If something is missing, you can buy it at the nearest radio store. You will have to spend a maximum of 300 rubles on components.
If diagram If assembled correctly, there is no need for additional configuration - it will be immediately ready for use.
You need to use the following electrical diagram:
Scheme
The positive thing is that if you install stabilizer to the desired radiator, then the battery is charged without fear that the charger will catch fire. But this certainly cannot be said about Chinese chargers, which suffer from this unpleasant consequence.
Operating principle – 4 nuances
- to start battery must be charged using direct current, which is determined by the resistance of resistor R4;
- after battery receives a voltage of 4.2 Volts, the device switches to DC charging;
- when the current drops to minimum values, the LED will stop lighting;
- current recharging lithium-ion battery, should not exceed 10% of the capacity of the entire battery. Thus, the service life of the batteries increases. If resistor R4 has a value of 11 ohms, then the circuit current should be 100 mA. If the resistance is 5 ohms, then the charging current should be 230 mA.
It is also important to know 3 nuances about “life extension” 18650
- If battery will need to be left unused for some time, it is advisable to store the batteries separately from the device that they will power. If a cell is fully charged, it will lose some of its charge over time. In the case when the element is charged very little, or is completely discharged, its performance may completely disappear. This is especially noticeable during periods of long hibernation.
- Storage 18650 should be carried out at a charge level that does not fall below 50%. Under no circumstances should the cell be allowed to be fully charged or overcharged. This equipment has no memory effect. Charging must be done until the charge is completely exhausted. This will extend the battery life.
- Battery Do not leave in too cold or hot areas. Suitable storage temperature is + 10 - + 25 degrees Celsius. If you place the battery in the cold, not only will the operating time decrease, but the chemical system will also deteriorate. Everyone has probably noticed that when using a mobile phone in winter, the charge batteries falls sharply.
How to avoid 4 mistakes when using and charging a lithium-ion battery
- In the event that you decide to recharge the lithium-ion battery using a store charger, you will have to make sure that it is not made in China. Typically, such devices are assembled from the cheapest materials, and the required technology is not always observed in them. As a result, this can lead to very sad consequences: fire and explosion.
- If you want to assemble it yourself device, then to charge the battery you need to use a current that is 10% of the battery capacity. The percentage may be higher, but not exceed 20%.
- When using ion batteries, do not violate the rules of storage and operation, otherwise overheating, fire and explosion may occur.
- If you follow all the rules operation, as well as the correct storage conditions, the battery life will be extended.
Top 3 Best Chargers for 18650 Battery
To ensure high-quality battery charging, you should purchase good devices, which is already loved by many users.
- Nitecore Digicharger D4 – suitable for charging multiple batteries at once. Extremely easy to use.
- Nitecore i2 is one of the best options for modern devices. Clear and easy to use.
- Basen B21 is a universal device for different types of batteries.
Lithium batteries (Li-Io, Li-Po) are currently the most popular rechargeable sources of electrical energy. The lithium battery has a nominal voltage of 3.7 Volts, which is indicated on the case. However, a 100% charged battery has a voltage of 4.2 V, and a discharged one “to zero” has a voltage of 2.5 V. There is no point in discharging the battery below 3 V, firstly, it will deteriorate, and secondly, in the range from 3 to 2.5 It only supplies a couple of percent of energy to the battery. Thus, the operating voltage range is 3 – 4.2 Volts. You can watch my selection of tips for using and storing lithium batteries in this video
There are two options for connecting batteries, series and parallel.
With a series connection, the voltage on all batteries is summed up, when a load is connected, a current flows from each battery equal to the total current in the circuit; in general, the load resistance sets the discharge current. You should remember this from school. Now comes the fun part, capacity. The capacity of the assembly with this connection is fairly equal to the capacity of the battery with the smallest capacity. Let's imagine that all batteries are 100% charged. Look, the discharge current is the same everywhere, and the battery with the smallest capacity will be discharged first, this is at least logical. And as soon as it is discharged, it will no longer be possible to load this assembly. Yes, the remaining batteries are still charged. But if we continue to remove current, our weak battery will begin to overdischarge and fail. That is, it is correct to assume that the capacity of a series-connected assembly is equal to the capacity of the smallest or most discharged battery. From here we conclude: to assemble a series battery, firstly, you need to use batteries of equal capacity, and secondly, before assembly, they all must be charged equally, in other words, 100%. There is such a thing called BMS (Battery Monitoring System), it can monitor each battery in the battery, and as soon as one of them is discharged, it disconnects the entire battery from the load, this will be discussed below. Now as for charging such a battery. It must be charged with a voltage equal to the sum of the maximum voltages on all batteries. For lithium it is 4.2 volts. That is, we charge a battery of three with a voltage of 12.6 V. See what happens if the batteries are not the same. The battery with the smallest capacity will charge the fastest. But the rest have not yet charged. And our poor battery will fry and recharge until the rest are charged. Let me remind you that lithium also does not like overdischarge very much and deteriorates. To avoid this, recall the previous conclusion.
Let's move on to parallel connection. The capacity of such a battery is equal to the sum of the capacities of all batteries included in it. The discharge current for each cell is equal to the total load current divided by the number of cells. That is, the more Akum in such an assembly, the more current it can deliver. But an interesting thing happens with tension. If we collect batteries that have different voltages, that is, roughly speaking, charged to different percentages, then after connecting they will begin to exchange energy until the voltage on all cells becomes the same. We conclude: before assembling, the batteries must again be charged equally, otherwise, when connected, large currents will flow, and the discharged battery will be damaged, and most likely may even catch fire. During the discharge process, the batteries also exchange energy, that is, if one of the cans has a lower capacity, the others will not allow it to discharge faster than themselves, that is, in a parallel assembly you can use batteries with different capacities. The only exception is operation at high currents. On different batteries under load, the voltage drops differently, and current will start flowing between the “strong” and “weak” batteries, and we don’t need this at all. And the same goes for charging. You can absolutely safely charge batteries of different capacities in parallel, that is, balancing is not needed, the assembly will balance itself.
In both cases considered, the charging current and discharge current must be observed. The charging current for Li-Io should not exceed half the battery capacity in amperes (1000 mah battery - charge 0.5 A, 2 Ah battery, charge 1 A). The maximum discharge current is usually indicated in the datasheet (TTX) of the battery. For example: 18650 laptops and smartphone batteries cannot be loaded with a current exceeding 2 battery capacities in Amperes (example: a 2500 mah battery, which means the maximum you need to take from it is 2.5 * 2 = 5 Amps). But there are high-current batteries, where the discharge current is clearly indicated in the characteristics.
Features of charging batteries using Chinese modules
Standard purchased charging and protection module for 20 rubles for lithium battery ( link to Aliexpress)
(positioned by the seller as a module for one 18650 can) can and will charge any lithium battery, regardless of shape, size and capacity to the correct voltage of 4.2 volts (the voltage of a fully charged battery, to capacity). Even if it is a huge 8000mah lithium package (of course we are talking about one 3.6-3.7v cell). The module provides a charging current of 1 ampere, this means that they can safely charge any battery with a capacity of 2000mAh and above (2Ah, which means the charging current is half the capacity, 1A) and, accordingly, the charging time in hours will be equal to the battery capacity in amperes (in fact, a little more, one and a half to two hours for every 1000mah). By the way, the battery can be connected to the load while charging.
Important! If you want to charge a smaller capacity battery (for example, one old 900mAh can or a tiny 230mAh lithium pack), then the charging current of 1A is too much and should be reduced. This is done by replacing resistor R3 on the module according to the attached table. The resistor is not necessarily smd, the most ordinary one will do. Let me remind you that the charging current should be half the battery capacity (or less, no big deal).
But if the seller says that this module is for one 18650 can, can it charge two cans? Or three? What if you need to assemble a capacious power bank from several batteries?
CAN! All lithium batteries can be connected in parallel (all pluses to pluses, all minuses to minuses) REGARDLESS OF CAPACITY. Batteries soldered in parallel maintain an operating voltage of 4.2v and their capacity is added up. Even if you take one can at 3400mah and the second at 900, you will get 4300. The batteries will work as one unit and will discharge in proportion to their capacity.
The voltage in a PARALLEL assembly is ALWAYS THE SAME ON ALL BATTERIES! And not a single battery can physically discharge in the assembly before the others; the principle of communicating vessels works here. Those who claim the opposite and say that batteries with a lower capacity will discharge faster and die are confused with SERIAL assembly, spit in their faces. 
Important! Before connecting to each other, all batteries must have approximately the same voltage, so that at the time of soldering, equalizing currents do not flow between them; they can be very large. Therefore, it is best to simply charge each battery separately before assembly. Of course, the charging time of the entire assembly will increase, since you are using the same 1A module. But you can parallel two modules, obtaining a charging current of up to 2A (if your charger can provide that much). To do this, you need to connect all similar terminals of the modules with jumpers (except for Out- and B+, they are duplicated on the boards with other nickels and will already be connected anyway). Or you can buy a module ( link to Aliexpress), on which the microcircuits are already in parallel. This module is capable of charging with a current of 3 Amps.
Sorry for the obvious stuff, but people still get confused, so we'll have to discuss the difference between parallel and serial connections.
PARALLEL the connection (all pluses to pluses, all minuses to minuses) keeps the battery voltage at 4.2 volts, but increases the capacity by adding all the capacitances together. All power banks use a parallel connection of several batteries. Such an assembly can still be charged from USB and the boost converter raises the voltage to the output 5v.
CONSISTENT connection (each plus to the minus of the subsequent battery) gives a multiple increase in the voltage of one charged can of 4.2v (2s - 8.4v, 3s - 12.6v, and so on), but the capacity remains the same. If three 2000mah batteries are used, then the assembly capacity is 2000mah.
Important! It is believed that for sequential assembly it is sacred that it is necessary to use only batteries of the same capacity. Actually this is not true. You can use different ones, but then the battery capacity will be determined by the LOWEST capacity in the assembly. Add up 3000 + 3000 + 800 - you get an 800mah build. Then the specialists begin to crow that then a less capacious battery will discharge faster and die. But it doesn’t matter! The main and truly sacred rule is that for sequential assembly, it is always necessary to use a BMS protection board for the required number of cans. It will determine the voltage on each cell and turn off the entire assembly if one is discharged first. In the case of a bank of 800, it will be discharged, the BMS will disconnect the load from the battery, the discharge will stop and the residual charge of 2200mah on the remaining banks will no longer matter - you need to charge.
The BMS board, unlike the single charger module, IS NOT A SERIAL CHARGER. Needed for charging tuned source of the desired voltage and current. Guyver made a video about this, so don't waste your time, watch it, it's about it as thoroughly as possible.
Is it possible to charge a series assembly by connecting several single charging modules?
In fact, under certain assumptions, it is possible. For some homemade products, a circuit using single modules, also connected in series, has proven itself, but EACH module needs its own SEPARATE POWER SUPPLY. If you charge 3s - take three phone chargers and connect each to one module. When using a single source - power short circuit, nothing works. This system also works as protection for the assembly (but the modules are capable of delivering no more than 3 amperes). Or, simply charge the assembly one by one, connecting the module to each battery until fully charged.
Battery charge indicator 
Another pressing problem is to at least know approximately how much charge remains on the battery so that it does not run out at the most crucial moment.
For parallel 4.2-volt assemblies, the most obvious solution would be to immediately purchase a ready-made power bank board, which already has a display showing charge percentages. These percentages aren't super accurate, but they still help. The issue price is approximately 150-200 rubles, all are presented on the Guyver website. Even if you are not building a power bank but something else, this board is quite cheap and small to fit into a homemade product. Plus, it already has the function of charging and protecting batteries.
There are ready-made miniature indicators for one or several cans, 90-100 rubles 
Well, the cheapest and most popular method is to use an MT3608 boost converter (30 rubles), set to 5-5.1v. Actually, if you make a power bank using any 5-volt converter, then you don’t even need to buy anything additional. The modification consists of installing a red or green LED (other colors will work at a different output voltage, from 6V and higher) through a 200-500 ohm current-limiting resistor between the output positive terminal (this will be a plus) and the input positive terminal (for an LED this will be a minus). You read that right, between two pluses! The fact is that when the converter operates, a voltage difference is created between the pluses; +4.2 and +5V give each other a voltage of 0.8V. When the battery is discharged, its voltage will drop, but the output from the converter is always stable, which means the difference will increase. And when the voltage on the bank is 3.2-3.4V, the difference will reach the required value to light the LED - it begins to show that it is time to charge.
How to measure battery capacity?
We are already accustomed to the idea that for measurements you need an Imax b6, but it costs money and is redundant for most radio amateurs. But there is a way to measure the capacity of a 1-2-3 can battery with sufficient accuracy and cheaply - a simple USB tester.
The lithium-ion battery is a worthy alternative to disposable batteries. Its purchase provides a chance not to have to buy new batteries for many months to come. The question of how to properly charge a Li-ion battery is of interest to those who have already ruined such batteries, or have heard that they are quite easy to kill.
We figure out how to charge a lithium-ion battery so that it serves for a long time and properly.
Li-ion batteries have a round or rectangular cross-section, their body is made of metal or a special film. Battery sizes and capacities vary. For 18650 the maximum capacity is 3400-3500 mAh. On some batteries you can find markings of over 4000 mAh; this indicates dubious quality and the manufacturer of the product. The actual power does not exceed 3400 mAh; often from unreliable manufacturers it is much lower.
The 18650 marking contains the following information: the first 2 digits (18) are the diameter in millimeters, the next 2 (65) are the length in mm, the last (0) indicates that the battery has a round cross-section.
Find out the charging time of your battery
Depending on the characteristics, different forms of chargers are required; the principle of their operation does not depend on the shape and volume of the lithium-ion battery.
General charging rules:
Li-ion battery
- make sure that it is a battery in front of you, and not a battery that cannot be recharged; it should be written “rechargeable”, which means “rechargeable”;
- When installing the battery into the device, observe the polarity;
- ensure disconnection from the network when 4.2V is reached; the automatic device will turn off itself, otherwise you will have to turn it off manually; In case there are no charging indicators, below is how long it takes;
- battery operating cycles within 25-90% capacity will significantly extend its service life;
- power supply at a lower current increases the service life of the battery; what current strength to choose, read below.
Charging time
How long it takes to charge a Li-ion 18650 battery depends on its capacity and current. The exact time is the ratio of the battery capacity to the current strength. When calculating, do not forget that 1 milliamp is equal to 1000 amperes. So, to charge a 18650 2600 mAh battery with a current of 1A, it will take 2 hours 36 minutes. If the current strength changes, this must be taken into account for the calculation.
Pre-charging stage
There are 3 stages. Pre-charging with reduced power DC provides voltages up to 2.8V and also pre-warms the lithium-ion battery. This power allows you to charge batteries discharged below 2.5V, as well as in conditions of low ambient temperature. During deep discharge, the procedure prevents overheating.
DC charging
The current value at this stage ranges from 20 to 50% of the battery capacity. With the accelerated version, it can be from 50 to 100% of capacity. Thus, a lithium-ion battery 18650 with a capacity of 3400 mAh should be charged throughout the entire stage with a current of 680 to 1700 mA, according to an accelerated scheme - from 1700 to 3400 mA.
It is important that the value does not change from the beginning to the end of the stage.
When the voltage reaches 4.2V, the battery capacity will be increased by 70-80%. Slow charging provides a higher rate, faster charging - less.
Constant voltage charging with falling current
The voltage is kept at 4.2(±0.3)V, the current value is monitored. Its strength will decrease as capacity increases. Charging will be completed when the current reaches 1-5% of the battery capacity.
At the end of charging, you need to disconnect the 18650 battery from the power supply, since prolonged exposure to voltage causes irreversible changes and the battery capacity decreases.
Selecting a charger
The described power principle is provided by modern chargers from time-tested brands. The device itself tests the charge level in the battery and ensures an effective filling process. At home, the user usually does not know what current to charge a Li-ion 18650 battery. This is not necessary; it is enough to have reliable equipment.
There are devices on sale with which their manufacturers promise to charge the battery especially quickly. Is the offer tempting? Hardly. Acceleration occurs due to an increase in current strength. The capacity of the lithium-ion battery as a result of charging is not high, the battery discharges quickly. Increasing the charging voltage significantly reduces the service life.
By purchasing a device that allows you to charge at a voltage no higher than 4.1V, you will extend the life of the battery. However, the charge capacity will decrease by 10%.
Summarizing the priorities when choosing a device, we are looking for slow, smooth charging, automatic process control, including automatic shutdown. We give preference to famous Japanese and Korean brands.
