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:

1. good capacity;
2. low self-discharge;
3. 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.

Review of chargers for 18650 lithium batteries

Modern man is helped by many gadgets. In particular, we use laptops, smartphones, cameras, tablets, etc. Most of these devices run offline on lithium batteries. Batteries make these devices truly mobile. One of the types of lithium batteries is 18650. They look like AA batteries, but they are larger in size. Such battery cells are present in laptop batteries, flashlights, and electronic cigarettes. It was the latter that made this type of battery especially in demand. For those who have such batteries, it is important to know how to charge them correctly. In this article we will talk about chargers (chargers) for 18650 batteries. We will talk about the general requirements for such devices, and also look at several examples of such chargers.

Charging for lithium 18650 batteries should produce an output of 5 V and a current of 0.5 to 1 of the rated capacity of the battery. That is, a lithium cell with a capacity of 2600 mAh must be charged with a current of 1.3-2.6 amperes. Manufacturers of lithium battery chargers make chargers that carry out the process in several stages.

The first stage of charging is carried out with a current of (0.2─1) from the value of the capacitance. In this case, the voltage is maintained at 4.1-4.2 volts (on one bank). This stage lasts a little less than an hour. The second stage takes place at constant voltage. Some manufacturers produce devices that implement pulse mode. This allows for faster charging.

Examples of chargers for 18650 batteries

The Nitecore Digicharger D4 charger is designed to charge a maximum of four batteries. The Nitecore brand has managed to establish itself by producing high-quality devices. D4 only confirms the positive reputation.

The Nitecore D4 charger has a high-quality, informative display that displays a lot of useful data. Here you can see the charging speed and time, cell voltage, and other similar data. Controls allow you to switch between four compartments and view information for all chargeable items. Thanks to this, you can view the status of the batteries at any time. Charging is universal and batteries of different form factors can be inserted into the compartments. Including 18650 format.

The charger sets the charging speed and time automatically. There are advantages to this, but there are also disadvantages. After all, sometimes finer manual adjustments may be required, but here in Nitecore D4 there is none. Features include an optimized method for charging IMR batteries. In addition, it is worth noting that charging is automatically interrupted at the end of the process for all supported battery types. This is a definite plus for this device.

Overall, Nitecore D4 can be recommended for daily use for those who have many mobile devices with different types of batteries. Among them are 18650 lithium batteries. The functionality of the device is quite wide, but for the convenience of beginners, fully automatic operation is provided. A good combination of price, features and build quality.

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.

How to properly charge a lithium-ion battery and significantly extend the life of 18650 batteries. What current should I use to charge a Li-Ion 18650 battery?

Batteries of this size have several important indicators:

• capacity (mAh – mAh)
• discharge current (A)
• charge current (A)
• maximum number of discharge cycles

In this article, I'll tell you about the last option and how this information can help you extend the life of your batteries.

Step 1: Full Discharge Cycles

What is a cycle?

When a battery is charged and then discharged, this is considered one cycle.

1. When charging lithium-ion 18650 batteries, the voltage rises to a maximum of 4.2 V, then drops to a range between 2 and 3 V, depending on the charge voltage limit specified in the datasheet of the specific cell.
2. Do not allow less than 3 V to preserve the battery life. This occurs with any process that requires battery power. These processes require current, which is provided by the battery, so it is discharged. Test equipment can also be used for discharge.
3. Use a dedicated charger to charge 18650 lithium-ion batteries.
4. How is the number of cycles calculated? The maximum number of full discharge cycles is determined by the difference between the capacity at the first charge (nominal) and the current charge level. For example, initially your phone was charged up to 3000 mAh, but now it is charged up to 2900 mAh, that is, up to 96% of the nominal capacity.
5. When this figure drops to 80%, the battery is said to have “died” (even if in fact it will survive another couple of thousand cycles).

• For a 3000 mAh battery, conditional “death” occurs at 80% of the nominal capacity.
• 80% of 3000 is 2400, so when the battery capacity drops to this value, it will be considered “dead”.
• Number of full discharge cycles for 18650 batteries
• Typically, modern batteries of this size have a cycle life of 300 to 500. This number can drop to 200 from overcharging or deep discharging. If the charge level drops below the minimum limit (A), the number of cycles may drop down to 50.
• Under optimal operating conditions, your battery's cycle life can exceed 500.
• Some manage to increase this number as much as 1000.

Step 2: Optimize Temperature

Deviation from these figures entails a decrease in the ability to hold a charge. A deviation of 10°C reduces the capacity by 20 or even 30 mAh.

Extreme temperatures (below 0° and above 70°C) lead to rapid degradation. Operating a battery at temperatures outside the designated limits will quickly damage the battery.

Never charge batteries at temperatures below 0, this will very quickly destroy the battery structure.

If you notice that the battery gets hot while using it, let it rest. During normal use the battery will not get very hot and its temperature will never rise above 60°C. If it heats up quickly, you're overloading it.

Step 3: Do not overcharge the battery (above 4.2V) or allow it to go into deep discharge (below 4.0V)

If you are more concerned about maintaining cycle count rather than capacity, then you may want to avoid charging the battery all the way.

Instead, you can charge it using a partial charge method - where you charge it to, for example, 3.8 V instead of the intended 4.2 V.

You will notice that the capacity has decreased, but if you also reduce the load, the number of cycles of your battery will increase. Overcharging will increase the battery's capacity, but it is dangerous and will shorten the life of your battery.

Step 4: Reduce the charging current (Amps)

Many chargers reduce the charging current. “Fast charging” takes place at a current of 1 A or higher. Although this will charge the battery faster, it will last significantly less. The graph shows how the charging current affects the number of full discharge cycles.

Step 5: Reduce Discharge Current (Amps)

When your phone is running low, as mentioned above, you can set the voltage limit. But you can also set the discharge current amperage. The higher the amperage, the lower the resulting capacitance.

High current discharge will also reduce the number of discharge cycles. Discharge the battery at low current whenever possible. All major electronics companies typically run discharge tests at only 0.5-0.8A.

Step 6: Increase the limit voltage

A logical continuation of the partial charging method is partial discharging. The partial discharge cycle, in contrast to the full discharge cycle, is little known. Its advantage is that by reducing the load on the battery, the number of charging cycles increases.

Instead of discharging to 2.8V (or the value specified in your battery's data sheet), you can discharge the battery to 3.2V.

Step 7: A little about battery chemistry

Batteries perform differently depending on their chemistry. Under optimal operating conditions, many 18650 sized cans can achieve cycle counts of 1000 or even higher.

The type of 18650 lithium-ion battery with the highest number of discharge cycles is LiFePO4 (lithium iron phosphate battery).

Lithium batteries (Li-Io, Li-Po) are the most popular rechargeable sources of electrical energy at the moment. 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 connection (all pluses to pluses, all minuses to minuses) maintains the battery voltage of 4.2 volts, but increases the capacity by adding all the capacities together. All power banks use parallel connection of several batteries. Such an assembly can still be charged from USB and the voltage is raised to an output of 5v by a boost converter.
CONSISTENT connection (each plus to minus of the subsequent battery) gives a multiple increase in the voltage of one charged bank 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 strictly 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 SMALLEST capacity in the assembly. Add 3000+3000+800 and you get an 800mah assembly. Then the specialists begin to crow that the less capacious battery will then 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 detect the voltage on each cell and turn off the entire assembly if one discharges first. In the case of an 800 bank, it will discharge, 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 a single charging module, IS NOT A sequential charger. Needed for charging configured source of the required voltage and current. Guyver made a video about this, so don’t waste your time, watch it, it’s about this in as much detail as possible.

Is it possible to charge a daisy chain assembly by connecting several single charging modules?
In fact, under certain assumptions, it is possible. For some homemade products, a scheme using single modules, also connected in series, has proven itself, but EACH module needs its own SEPARATE POWER SOURCE. If you charge 3s, take three phone chargers and connect each to one module. When using one 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 critical 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.