Lithium-ion batteries are not as picky as their nickel-metal hydride counterparts, but they still require some maintenance. Adhering to five simple rules, you can not only extend the life cycle of lithium-ion batteries, but also increase the operating time of mobile devices without recharging.
Do not allow full discharge. Lithium-ion batteries do not have a so-called memory effect, so they can and, moreover, need to be charged without waiting for discharge to zero. Many manufacturers calculate the life of a lithium-ion battery as a number of full discharge cycles (up to 0%). For quality batteries, this is 400-600 cycles... To extend the life of your lithium-ion battery, charge your phone more often. Optimally, as soon as the battery charge drops below the 10-20 percent mark, you can put the phone on charge. This will increase the number of discharge cycles to 1000-1100
.
Experts describe this process by such an indicator as Depth Of Discharge. If your phone is up to 20% discharged, then the Depth of Discharge is 80%. The table below shows the relationship between the number of discharge cycles of a lithium-ion battery and the Depth of Discharge:
Discharge every 3 months. A full charge for a long time is just as harmful to lithium-ion batteries as being constantly discharged to zero.
Due to the extremely unstable charging process (we often charge the phone as necessary, and where it works, from USB, from an outlet, from an external battery, etc.), experts recommend completely discharging the battery once every 3 months and then charging it to 100% and holding it on charge 8-12 hours. This helps to reset the so-called high and low battery charge flags. You can read more about this.
Store partially charged... The best condition for long-term storage of a lithium-ion battery is between 30 and 50 percent charge at 15 ° C. If the battery is left fully charged, its capacity will decrease significantly over time. But the battery, which has been gathering dust on the shelf for a long time discharged to zero, most likely is no longer a tenant - it's time to send it for recycling.
The table below shows how much capacity remains in a lithium-ion battery depending on storage temperature and charge level when stored for 1 year. 
Use the original charger. Few people know that in most cases the charger is built directly into mobile devices, and an external power adapter only lowers the voltage and rectifies the current of the household power supply, that is, it does not directly affect the battery. Some gadgets, such as digital cameras, do not have a built-in charger, and therefore their lithium-ion batteries are inserted into an external “charger”. This is where the use of an external charger of questionable quality instead of the original one can negatively affect the performance of the battery.
Do not overheat. Well, the worst enemy of lithium-ion batteries is high temperature - they cannot stand overheating at all. Therefore, do not expose mobile devices to direct sunlight or leave them in the immediate vicinity of heat sources such as electric heaters. Maximum permissible temperatures at which lithium-ion batteries can be used: from –40 ° C to + 50 ° C
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The advantage of rechargeable batteries over conventional batteries is that the service life of the former is much longer. But in order to take advantage of this advantage, you need to know how to charge the battery depending on its type and characteristics.
Battery types
To date, quite a few different battery devices have been invented. The principle of operation of any of them is that electrochemical reactions take place inside, as a result of which charged particles appear, a potential difference (voltage) and an electric current arise. The reactions inside the battery are reversible and can therefore be charged. To do this, it is necessary to pass current through it in the opposite direction. The number of recharges varies depending on the type of device and how well you use it.
Batteries can be connected in parallel or in series to form a battery. In this way, the current or voltage is increased, respectively. Depending on the chemical composition of the electrodes and electrolyte, the following most popular types of batteries are distinguished:
- lead acid;
- nickel-cadmium (cadmium is the anode);
- nickel metal hydride (metal hydride is the anode);
- nickel-zinc;
- lithium-ion;
- advanced lithium polymer;
This is far from the entire list, so you may come across another type, however, these are most often found in the devices that we use in everyday life.
All batteries can be charged using devices specially provided for this, therefore, a charger is usually purchased along with the device or battery. If you do not want to buy a charger, then you have the opportunity to contact the service technical center. These services are usually provided there. Some batteries can also be charged from a DC power source. In this case, the voltage of the source should be large, and the current should be limited to a value of 0.1 of the battery capacity. Exceeding the charge level is undesirable.
Charging features
A battery can only be used to its fullest if it is properly charged and operated. Let's consider in more detail how to charge a battery of one type or another.
Lead
Lead-acid batteries are installed in cars and other vehicles, used as an uninterruptible power supply, as well as for recharging other batteries in emergency situations. They are distinguished by their reliability and unpretentiousness. Car owners need to know how to properly store and recharge their car's power supply.
They take a long time to discharge. At 20 ° C, they can discharge by only 40% in a year. However, it is necessary to charge them for a long time - almost a day. Lead-acid batteries can be charged with direct current (it should be 0.1-0.2 capacity, usually indicated on the case), or with constant voltage (for a 12 volt battery, it is 14.5 volts).
Pulse and transformer chargers are used, which in turn can be automatic or conventional. Charging should take place in a ventilated area or outdoors as explosive gas is generated and should not accumulate.
- First, check the electrolyte level in each battery and top up if necessary.
- The charger is connected to the terminals and the current is set (see value above).
Maintenance-free batteries are charged with constant voltage. The optimum charging temperature should be around 20 ° C. Proper storage of the car battery must be fully charged, clean and in a cool place.
Nickel
Nickel-cadmium and nickel-metal hydride batteries are widely used in construction tools, technical equipment and some types of electric vehicles. Many owners of power tools are interested in how to properly charge them.
A distinctive feature of nickel batteries is the memory effect. If the battery is not completely discharged, and you started charging it, then later it will not give up the entire charge, but only part of it (up to the last limit), and will no longer work. The battery seems to remember that it was not completely discharged the last time, and its capabilities are reduced.
For a nickel battery to work as long as possible, it must be completely discharged and then fully charged. This is especially true for nickel-cadmium devices. Note that there are chargers that are equipped with a "re-discharge" function. If the battery has lost its capacity, then you can try to fully recharge it 3 times in a row.
The nickel battery is also not beneficial to its overcharging, therefore it is necessary to disconnect it from the charger in a timely manner. The end of the process is indicated by an increase in the temperature of the case or an indicator light. Nickel-cadmium batteries will properly be stored in a discharged state, but nickel-metal hydride batteries only fully charged.
Nickel-zinc power sources usually replace finger batteries, they can work in frost and hot weather, they are environmentally friendly and fire safe. They have no memory effect, but they are characterized by a small number of charge / discharge cycles - about 300. They can be charged using a special or universal charger.
Lithium
Nickel sources are being replaced by more modern lithium sources. Lithium-ion and more advanced lithium-polymer devices are used to power mobile phones, laptops, tablets, electric vehicles, and can be installed on construction tools (drills, screwdrivers, etc.).
The advantage of lithium batteries is that they can deliver high current and charge very quickly. In addition, they practically do not discharge while in storage. They have practically no memory effect, but over time they age - they lose about 20% of their capacity in a couple of years. That is why it is recommended not to buy them in stock and to check the release date when purchasing.
Lithium devices are very capricious, so it is important to use and charge them correctly.
- It is advised to store lithium batteries charged at 60-40%.
- Do not leave them in frost or hot places, especially while charging.
- High and low temperatures render the device unusable.
- A deep discharge of a lithium current source and an increase in voltage on it must not be allowed, since it can completely fail.
Due to the design features, lithium batteries can only be charged using special chargers. There are universal chargers suitable for different types of batteries, and chargers designed only for lithium sources. The latter cost significantly less, while the former requires customization.
The popularity of lithium batteries is growing all over the world, and they are gradually replacing nickel, even though they are finicky. This is due not only to the high capacity and the large potential number of recharges. Lithium devices are safer from an environmental point of view, which is receiving increased attention today.
Batteries
How to charge a li ion 18650 battery? How to properly operate such a battery. What are lithium-ion power supplies to be afraid of and how can such a battery extend its service life? Similar questions can arise in a wide variety of electronics industries.
And if you decide to assemble your first flashlight or electronic cigarette with your own hands, then you definitely need to familiarize yourself with the rules for working with such power sources.
A lithium-ion battery is a type of electric current accumulator, which since 1991, after being presented to the market by SONY, has become widespread in modern household and electronic equipment. Such batteries are used as a power source in cell phones, laptops and camcorders, as a power source for an electronic cigarette and an electric vehicle.
The disadvantages of this type of battery start with the fact that the first generation lithium ion batteries were the explosion in the market. Not only literally, but also figuratively. These batteries exploded.
This was explained by the fact that a lithium metal anode was used inside. In the process of numerous charges and discharges of such a battery, spatial formations appeared at the anode, which led to the closure of the electrodes, and as a result, to a fire or explosion.
After this material was replaced with graphite, this problem was eliminated, but there could still be problems on the cathode, which was made of cobalt oxide. If the operating conditions were violated, or rather overcharging, the problem could recur. This was corrected with the beginning of the use of lithium-ferro-phosphate batteries.
All modern lithium-ion batteries prevent overheating and overcharging, but the problem of loss of charge at low temperatures remains.
Among the indisputable advantages of lithium-ion batteries, I would like to note the following:
- high battery capacity;
- low self-discharge;
- no need for maintenance.
Original chargers
The charger for lithium-ion batteries is quite similar to the charger for lead acid batteries. The only difference is that the lithium-ion battery has very high voltages per cell and tighter voltage tolerance requirements.
Such a battery is called a can because of the external similarity with aluminum cans for drinks. The most common battery of this form is the 18650. The battery received this designation due to its dimensions: 18 millimeters in diameter and 65 millimeters in height.
While some inaccuracies in indicating the boundary voltages during charging are permissible for lead-acid batteries, the situation with lithium-ion cells is much more specific. During charging, when the voltage rises to 4.2 Volts, the voltage supply to the cell should stop. The margin of error is only 0.05 volts.
Chinese chargers that can be found on the market can rely on batteries based on different materials. Li-ion, without prejudice to its performance, can be charged with a current of 0.8 A. In this case, you need to very carefully monitor the voltage on the bank. It is advisable not to allow values above 4.2 Volts. If there is a controller in the assembly with the battery, then there is nothing to worry about, the controller will do everything for you.
The most ideal charger for lithium-ion batteries is a voltage regulator and current limiting device at the beginning of the charge.
Lithium needs to be charged with a stable voltage and current limiting at the beginning of the charge.
Homemade charger
To charge the 18650, you can buy a universal charger, and not be tormented by the question of how to check the necessary parameters with a multimeter. But such an acquisition will cost you a pretty penny.
The price for such a device will vary around $ 45. But you can still spend 2-3 hours and assemble the charger with your own hands. Moreover, this charger will be cheap, reliable and will automatically disconnect your battery.
The parts that we will use today to create our charger are available to every radio amateur. If a radio amateur with the necessary parts is not at hand, then on the radio market you can buy all the parts for no more than 2-4 dollars. The circuit, which is assembled correctly and neatly assembled, starts working immediately and does not need any additional debugging.
18650 battery charging circuit.
On top of that, by installing the stabilizer on a suitable radiator, you can safely charge your batteries without fear of overheating and catching fire. The same cannot be said about Chinese chargers.
The circuit works quite simply. First, the battery needs to be charged with constant current, which is determined by the resistance of the resistor R4. After the battery has a voltage of 4.2 Volts, constant voltage charging begins. When the charging current drops to very low values, the LED in the circuit will turn off.
The currents recommended for charging lithium-ion batteries should not exceed 10% of the battery capacity. This will extend the life of your battery. When the value of the resistor R4 is 11 Ohm, the current in the circuit will be 100 mA. If you use a 5 ohm resistance, then the charging current will already be 230 mA.
How to extend the life of your 18650
Disassembled battery.
If you have to leave your lithium-ion battery without work for a while, it is better to store the batteries separately from the device that they power. A fully charged cell will lose part of its charge over time.
An element that is very little charged, or discharged at all, can permanently lose its performance after a long hibernation. Storing the 18650 at a charge level of about 50 percent is optimal.
Do not allow the cell to be completely discharged and overcharged. Lithium-ion batteries have no memory effect at all. It is advisable to charge such batteries until the moment when their charge is completely dry. This can also prolong the battery life.
Lithium Ions do not like heat or cold. The optimal temperature conditions for these batteries will be in the range from +10 to +25 degrees Celsius.
Cold can not only reduce the operating time of an element, but also destroy its chemical system. I think each of us noticed how the charge level in a mobile phone quickly drops in the cold.
Conclusion
Summarizing all of the above, I would like to note that if you are going to charge a lithium-ion battery using a store-made charger, pay attention to the fact that it is not made in China. Very often, these chargers are assembled from cheap materials and the necessary technology is not always observed in them, which can lead to undesirable consequences in the form of fires.
If you want to assemble the device yourself, then you need to charge the lithium-ion battery with a current that will be 10% of the battery capacity. The maximum may be a figure of 20 percent, but this figure is already undesirable.
When using such batteries, it is worth following the rules of operation and storage in order to exclude the possibility of an explosion, for example, from overheating, or failure.
Compliance with the conditions and rules of operation will extend the life of the lithium-ion battery, and as a result - save you unnecessary financial costs. The battery is your helper. Take care of her!
Lithium batteries are increasingly entering our life to replace morally and physically obsolete nickel metal hydride batteries. Like many cool innovations, lithium batteries require special care in order to maximize their service life, and the user does not suffer from an accident. In this issue of the alexgyver channel, you will learn how to charge and a few more important points regarding the use and storage of lithium batteries.
There are many types of lithium batteries. The most popular lithium-ion, used in smartphones, laptops, screwdrivers, small digital technology. Recently, it has been gaining popularity as a replaceable power source for flashlights and other devices.
This is a lithium battery of 18650 format. There is a 14500 finger format. Do not confuse with ordinary fingers, because lithium fingers have a voltage of 4 volts, and normal ones are 1.5.
Lithium polymer batteries are used in modern smartphones as well as in radio-controlled toys, because they are capable of delivering fabulously high currents.
Usage
We bought a battery. In order for it to reach its full capacity, it is advisable to swing it. First discharge, then charge and repeat this cycle two more times. Lithium batteries do not have a memory effect, but the numbers speak for themselves.
As for the voltage. Do not exceed the minimum and maximum voltage on the battery, otherwise it will lose capacity and may catch fire or even explode. Most devices are equipped with a dedicated battery charge and discharge controller. Moreover, there is a protected version of the 18650. They are 5 millimeters longer than usual due to the fact that they have a controller. These are designated 18700 and are not afraid of overcharge and overdischarge. But the usual ones need to be used wisely.
If you are making any homemade device, be sure to connect the batteries through the module.
It costs only 25 rubles, but it can save your project and charge the battery from the micro usbi port.
Discharged to 80 percent? Charge! It won't make him any worse.
No need to make the battery work at full volume. At the same time, it is recommended that lithium batteries be fully discharged before being cut off about once every three months. And put it on charge immediately. This will help keep the upper and lower charge limits in good shape. And do not forget that a loaded, over-discharged lithium battery is capable of spontaneous combustion and even explosion. It can also happen if you recharge to a voltage that is higher than the maximum. Also, do not exceed the maximum discharge current. This will damage the battery.
It must be remembered that the higher the discharge alone, the more the voltage drops. For example, the battery is fully charged to four volts. We begin to load it with a large load and the voltage will already be three volts. And this can lead to unpredictable consequences for your device.
One more point. The higher the discharge current, the lower the battery capacity. Let it have a capacity of 3 amperes per hour. This means that he will be able to give a current of 3 amperes for 1 hour. It is logical to assume that he will be able to give 6 amperes for half an hour and 12 amperes in 15 minutes. But this is not the case. It will deliver a large current in much less time.
It is also very important to remember the temperature. At temperatures above 45 degrees, the lithium-ion battery begins to degrade and loses its capacity, and irreversibly. That is why it is strictly forbidden to solder them directly. Use cheap holders. If you need to assemble a compact battery assembly, then contact welding is needed.
Battery capacity also varies with temperature. For example, after charging the battery in a warm place, we have a 100 percent charge. We go out into the cold - let's say 80 percent. But if you charge it in the cold to 100 percent, and then go into the heat, the charge will be over one hundred percent. This is very damaging to the battery. So think a hundred times before charging in the cold.
What about survivability? Good lithium batteries last from five hundred to eight hundred charge-discharge cycles, after which their capacity drops by 20 percent of the original.
Storage.
Lithium batteries have such an unpleasant feature as a limited shelf life. That is, they begin to gradually deteriorate immediately after production, regardless of whether they are working or just lying on the shelf. Therefore, it makes no sense to stock up on spare batteries for the future. At the same time, the battery lying on the shelf gradually discharges, and when its charge drops below the minimum and it lasts a little longer, you will get a piece of iron. If you do not plan to use the battery for long enough, then remember. The battery is best at 40 to 50 percent charge. It is with this charge that they are sold. Temperature also affects storage. The higher it is, the faster the battery will self-discharge. Therefore, the author of the video keeps his batteries in the refrigerator.
Buy 18650 batteries the cheapest from the Chinese.
Then from 6 minutes on the video.
Source: youtu.be/qxqdrNkO0oU
Long-term storage of lithium-ion batteries
The power tool on lithium-ion batteries has become a part of our lives for a relatively long time. Gradually, electric transport is becoming a common means of transportation. Including for photographers. It is convenient to travel around the cities on an electric scooter, outside the city on an electric bike. Photographers are not interested in sports, we need a comfortable and not fast movement, when you can calmly look around in search of subjects.
And since a significant percentage of the price of all these wonderful and useful vehicles are lithium-ion batteries, care must be taken to ensure that they last as long as possible.
Long-term storage without degrading the performance of lithium-ion batteries is not an easy procedure. The problem with these cells is that, unlike lead acid batteries, they don't like to be stored for more than a few months fully charged. They need to be stored at 40-50% charge. Storing lithium-ion cells at 100% charge for long periods of time accelerates their degradation. Also, an important point is that half-discharged batteries do not explode (see video).
It is advisable to store batteries at temperatures around zero degrees. The relative humidity is not particularly important, around 50% is recommended. Self-discharge is not a big problem as long as the lithium-ion battery is not left unattended for so long that it is completely discharged. In this case, you can simply throw it away.
Every 6 months or so, you should check your batteries and charge them to 40-50%. When charging to this level, it is easiest to use a timer. If you have a 10 Ah battery and need to charge it approximately 20% using a 2 Amp charger, that means you should charge it within an hour (2 Ah / 2 Amp charger = 1 hour).
Approximate capacity losses depending on the charge level and temperature during storage of the battery are given below:
0 ° С - loss of capacity during storage of the battery with a 40% charge level - 2% / year
25 ° С - loss of capacity during storage of a battery with a 40% charge level - 4% / year
40 ° С - loss of capacity during storage of the battery with a 40% charge level - 15% / year
60 ° С - loss of capacity during storage of the battery with a 40% charge level - 25% / year
0 ° С - loss of capacity during storage of the battery with a full charge - 6% / year
25 ° С - loss of capacity during storage of the battery with a full charge - 25% / year
40 ° С - loss of capacity during storage of the battery with a full charge - 35% / year
60 ° С - loss of capacity during storage of the battery with a full charge - 40% / year
While some people store their lithium-ion batteries in the refrigerator, this is not recommended because the humidity inside your refrigerator can be quite high, which can cause corrosion problems on the connections and BMS. The best place to store them is cool, dry, and out of the reach of gnawing animals. A rat can easily gnaw through the shell and it will end in the same way as when a battery is damaged from a shock.
Never store lithium-ion batteries in your car, where the temperature can be very high on summer days.
Lithium-ion, or Li — Ion, the battery is necessary to maintain the smooth operation of a wide variety of equipment. These rechargeable batteries run smartphones, tablets, laptops, drills, flashlights and starting-charging batteries. Such widespread distribution of these models is explained by the high energy consumption and small size of these elements. In addition, Li-Ion batteries are rated for 300-400 cycles. In modern devices, this figure is up to 600 such cycles.
But in some cases, batteries fail much faster, the main reason for this phenomenon is considered to be the wrong mode of use. Therefore, it is so important to know how to properly charge a lithium-ion battery and what this device is.
Features of work
Typically a Li-Ion battery is a prismatic or cylindrical body made of aluminum or steel. Inside there is a package of electrodes, and separators are located. The cathode is any of the lithium oxides: lithium nickelate (LiNiO2) or cobaltate (LiCoO2). For these purposes, lithium ferrophosphate (iFePO4) and lithium manganese spinel (LiMn2O4) can be used. The anode is made of graphite, graphene and other carbonaceous compounds.
The process of charging and discharging the battery follows the principle of a rocking chair. In the course of work, lithium ions are transferred from one electrode to another. During discharge, lithium is extracted or deintercalated from the carbon material at the negative electrode and intercalated into the oxide at the positive electrode. When the batteries are being charged, everything happens in reverse order. In a prismatic body, electrodes and separators are folded in the form of rectangular plates, which provides an increased packing density. In cylindrical batteries, the contents are rolled up. Another option is to roll into an elliptical spiral. This makes it possible to combine both modifications.
Although many batteries can operate in the -40 ° C to + 50 ° C range, keep in mind that capacity and performance will vary depending on the ambient temperature. In cold weather, the capacity drops and the battery may be discharged. An increase in temperatures leads to a decrease in the resource and characteristics of the device. Therefore, do not store batteries in the sun, near electric heaters or other heat sources.
Note! All lithium batteries do not have a common standardization system. Models with the same specifications may differ. Therefore, the use of third-party ionic batteries by devices may damage the battery itself and all equipment.
The battery charger may work differently. In some equipment, the element that provides the very charging of li-ion batteries is built into the battery, in the other - the device does not have such a gadget. In the first case, the provided mains adapter is required to lower the voltage and rectify the current. Many mobile devices are charged this way. If we are talking about digital cameras, then the lithium battery is powered by an external charger. Using the wrong adapter will at best simply not charge the battery, and at worst will damage both the camera and the battery.
What does the battery charge depend on?
Some battery options are equipped with control elements that do not allow the critical values of the charge to go over. If the value is higher, the element will cut off the flow of current, and if it is lower, it will stop supplying the equipment. This avoids excessive heating and short circuits. If the power of the smartphone or tablet shows 10-20 percent, then the device should be put on charge. After the indicators have reached the maximum one hundred percent, you need to leave the equipment on charge for another one and a half or even two hours. Otherwise, the device will actually be charged only 70-80 percent.
But the rules say that you shouldn't charge the batteries to the maximum all the time. Manufacturers knowingly set maximum rates at 80 percent. This is due to the fact that during overcharging, oxygen is more actively evolved at the cathode, and a mossy deposit of lithium metal with a high electrolyte capacity is formed on the carbonaceous part. This increases the likelihood of thermal runaway, a subsequent increase in pressure and, as a result, destruction and even fire of the battery.
Of course, the latter happens quite rarely, but a decrease in battery life with constant overcharging is inevitable. If the equipment is not brought to full discharge, the number of work cycles can increase to one and a half thousand.
Note! The only option in which a decrease in the service life at maximum charging does not occur is Li-ion rechargeable batteries with manganese. The addition of manganese leads to a significant slowdown in the reaction of oxygen evolution and metallization of the anode. In such devices, controllers are not provided.
On the other hand, in order to prolong the life of the battery, it is sometimes necessary to bring the battery to a full discharge. This is due to the fact that it is quite difficult to constantly monitor the state of charge. The lack of periodicity of charging leads to the fact that the readings of the minimum and maximum charge, which were originally laid down in the controller, get lost. Gradually, the device begins to receive inaccurate data on the amount of charge. Bringing the battery to full discharge will lead to zeroing the controllers and fixing the minimum value. The next step is to charge the equipment as long as possible, approximately 8 to 12 hours. During this time, the controller will update the maximum value and the battery will stabilize.
If you plan not to use the battery for a long time, then you should:
- charge the device by 30-50%;
- provide a storage temperature of approximately 150C;
- place the equipment in a dry place.
Fully discharged batteries lose their performance during prolonged periods of inactivity and stop working. If you put a battery with 100% charge in storage, then in the process, a significant part of the capacity will be lost.
Attention! Cobalt is hazardous to the environment and humans; therefore, old batteries must be disposed of.
General charging rules
If you need to charge the battery in the car, then you need to use special chargers. The plus is connected to the positive terminal, and the minus to the negative. The regulator is set to minimum and left for several hours. A full charge corresponds to the indicators "0" or the green indicator.
Let's highlight the basic principles of how to properly and harmlessly charge and use lithium-ion batteries:
- You should not constantly wait for the complete discharge of the battery;
- In normal mode, charge the Li-ion battery at 10-20% charge;
- It is necessary to use only the standard charger;
- The cycle from full to maximum charge should be carried out once every 2-3 months;
- Keep batteries partially charged;
- Overheating and significant cooling of the equipment should be avoided.
Let's consider how to charge via a USB cable from a computer, because a USB adapter is often supplied with a smartphone. It is important to consider here that the charging speed will differ from the usual one. This is due to the fact that charging via the PC port is limited to 0.5 amperes.
If charging takes place through an adapter from a cigarette lighter in a car, you should carefully compare the characteristics of a standard adapter and a new one. Typically for smartphones, the value is 1 ampere, and for tablets, 2 amperes is required.
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