Changing the batteries in an electric screwdriver for lithium batteries

Learn how to convert an electric screwdriver to lithium-ion batteries with your own hands

the electric screwdriver is so tightly squeezed into the life of modern man that no repair or construction work at home and at work can do without it. The main convenience of the tool is its mobility, which is provided by a removable self-contained battery. That is why the device in question and received the name “cordless electric screwdriver“. Often in operation there is a question of how to remake the battery of an electric screwdriver, because nickel-cadmium batteries have a big disadvantage compared to lithium batteries. it is a low service life. In order not to buy a new electric tool with a lithium battery, you can upgrade the old battery by replacing the nickel-cadmium banks in it.

Electric screwdriver portability is achieved by using an independent power source. The source of the battery is a rechargeable battery, which works in the same way as a watch or remote control battery. Only a battery for power tools has a voltage several tens of times greater than that of an ordinary thumbtack battery.

The battery powers the electric screwdriver motor. As the electric motor armature rotates, torque is transmitted to the gearbox. A reduction gear reduces or increases the rotation speed (depending on the mode set) of the working body, the chuck, in which the bits are fixed. The independent power source as a battery in an electric screwdriver is a key element, without which the work of the device is simply impossible.

Often owners of inexpensive screwdrivers are faced with such a situation as a rapid discharge of the battery. The reason for this is the material of manufacture of the independent power supply. There are three basic types of batteries for an electric screwdriver:

  • Nickel-cadmium. the simplest, least expensive and short-lived. Another disadvantage of this material is a small charge reserve
  • Nickel-metal hydride batteries are an improved version of cadmium batteries that are more resistant to frequent charging and discharging (but they also discharge quickly). Exposure to low temperatures negatively affects the duration of operation of the source
  • Lithium-ion batteries are a new era of batteries that not only hold a charge for a long time (slow discharge due to high capacity), but can also last for at least 10 years

Often owners only after buying an electric screwdriver, which comes with a nickel-cadmium battery, realize that “you should have chosen a power tool with a lithium battery”. The reason for buying a power tool with a nickel-cadmium source is also easy to explain, because with such a battery the device is several times cheaper. If you don’t believe me, you can compare the price of screwdrivers in the online store Cylinder.

Nickel-cadmium and metal hydride. why replace them

One of the very first batteries to be used in power tools were nickel-hydride sources. The advantages of such devices include an optimal reserve capacity and low tank heating in comparison with hydride sources. In addition, such sources are inexpensive, and yet effectively cope with their main task when properly applied.

The advantages of nickel cadmium devices include

  • Low risk of overheating compared to hydride technology
  • Nickel cadmium sources are contained within a metal housing, which provides a high degree of stability and tightness
  • If properly operated, a nickel-hydride battery will last at least 3-5 years, but precisely because the device has to be used frequently in extreme conditions, the battery life decreases dramatically from the first day of purchase
  • Low cost, which makes such devices in demand
  • Not afraid of deep discharge

To extend the service life of the battery, not to ask yourself how to convert the battery of an electric screwdriver to lithium, it is necessary to follow the simple instructions for the use of Ni-Cd batteries:

  • You can and should use the tool until the battery is completely discharged
  • Charge the source until the capacity is completely replenished
  • Unlike lithium batteries, it is better to store cadmium batteries in a discharged state
  • The “memory effect” is a disadvantage, but it can be easily eliminated by repeating three “charge-discharge” cycles

Hydride batteries appeared after the cadmium ones, but they did not become very popular, as they quickly lose their charge, and they are not suitable for high-power models of screwdrivers. Hydride batteries have no “memory effect” and are less harmful to the environment than cadmium batteries. If your battery, which consists of cadmium or hydride sources, sooner or later it will be necessary to replace it. Buy a new battery for an electric screwdriver of a little-known brand or outdated model is almost impossible, so it becomes necessary to upgrade the old one. From the old cadmium battery can be made even better, but to do this you need to understand how to remake the battery electric screwdriver.

Types of batteries for an electric screwdriver

Almost all modern models of electric screwdrivers have the same structure of the battery pack. elements in series connected in a single chain. Their shape, dimensions and rating are always the same. Together, they create the final voltage of the appliance. The only difference between them is observed in capacity. This makes them easy to change and replace.

As a rule of thumb, there are 3 main varieties of batteries used:

Each unit is rated at 1.2 volts. Their main advantages are expressed in the following:

  • Availability due to prevalence and low price.
  • Resistant to negative ambient temperatures.
  • Preservation of performance when stored in a discharged state.

Disadvantages are manifested in the small capacity, as well as a number of factors such as:

In addition, due to the toxicity of the production cycle, this type of battery is produced by manufacturers in the 3rd world, which itself can manifest itself in factory defects and low quality.

Batteries of this modification provide a voltage of 1.2 V. Many people prefer them as an alternative to failed units when a battery for an electric screwdriver needs to be repaired. This is primarily due to the high quality, as the production line for trimmer does not contaminate the environment, and therefore the technology is widely used in developed countries by well-known manufacturers.

In addition, they have the following number of advantages:

  • Minimal memory effect.
  • Low self-discharge coefficient.
  • Higher capacity. as compared to the above variety.
  • Maximum operating range of charge-discharge cycles.

The disadvantages are the high cost, impossibility of use at low temperatures and deterioration of the characteristics when stored discharged for a long time.

Batteries of this variety have a nominal capacity of 3.6V. The main advantages are as follows

  • High capacity.
  • Several times longer range of operating cycles compared to other modifications.
  • No memory effect.
  • Slight self-discharge.
  • Possibility of reducing the weight of the battery pack. due to the need for fewer cells in the circuit due to their greater capacity and potential.
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The disadvantages are represented by the maximum price and the limited validity. Already after 3 years, batteries lose most of their capacity due to the chemical decay of the filler.

Please note! The main reason of breakage of a screwdriver is exactly the failure of the battery, or more precisely, the loss of rating or capacity of its individual elements. Thermistor failure, contact disconnection and other causes are extremely rare.

Fault detection

Due to the fact that the power supply is a chain of series-connected elements, it is required to determine which particular member has failed in order to perform its replacement to restore the battery performance of an electric screwdriver. Since one bad link de-energizes the whole chain.

For this purpose, the following algorithm of actions is applied:

  • The battery is installed in the charger until the charging signal is received.
  • The battery pack is disassembled.
  • Measure with a voltmeter the voltage of each battery.
  • Marks are put on all elements, which are not rated as normally working. For example, nickel cadmium batteries give out 1.1 or 1.0 volt instead of the 1.2 volt that they should.
  • The appliance is then assembled and turned on until the motor power is noticeably reduced.
  • Then all cells should be disassembled and the voltage of all cells should be measured.

Banks that have a nominal loss of 0.4 volts or more in comparison to normal cells are not suitable for further use and must be replaced.

The battery for an electric screwdriver consists of a chain of cells connected in

Tip! An alternative method of creating a load before testing the battery is to connect a light bulb of an appropriate rating. When the lamp begins to dim, the battery cells can be checked for differences in rating.

Fault location

Due to the fact that the power supply is a chain of series-connected elements, it is required to determine which particular member has failed in order to perform its replacement to restore the battery performance of an electric screwdriver. As one broken link de-energizes the whole chain.

batteries, electric, screwdriver, lithium

For this purpose the following algorithm is used:

  • The battery is placed in the charger until a charging signal is received.
  • Dismantle the battery block.
  • We measure the voltage of each bank with a voltmeter.
  • The marks are put on all the elements, the nominal value of which is lower than the normally working. For example, the nickel-cadmium ones give out 1.1 or 1.0 volt instead of the 1.2 volt.
  • Then the device is assembled and turned on until the motor power is noticeably reduced.
  • After that the battery is disassembled again and the voltage of all cells is measured.

The banks with nominal loss of 0.4 volt or more in comparison with normal ones are not suitable for further operation and must be replaced.

A battery for an electric screwdriver consists of a chain of cells connected in series

Tip:! An alternative way to create a load before testing the battery is to connect a light bulb of the appropriate rating. When the lamp begins to dim, the battery cells can be checked for differences in rating.

Repair possibilities

When it comes to a failed lithium-ion battery, the only way to get the battery of an electric screwdriver back working is to replace it with a new one. This is the best possible option in this case, since there is no memory effect in this type of battery and the cause of their failure is related only to chemical decomposition of the filler. But the cause of the malfunction may also be hidden in the control circuitry of the appliance.

Therefore, there are two ways to accurately determine the cause of the breakdown:

  • Install another, serviceable control circuit, and try to run the device. If the test method helped, then the cause is exactly a circuit failure.
  • Using an adjustable charger, connect the bank to a current of 4 V and 200 mA. When the nominal value rises to the specified 3.6 volts, it indicates that the system is fully operational. The cause of the failure must be sought either in the neighboring power elements or in the control circuitry.

To identify the faulty cell, each can of the battery pack of an electric screwdriver needs to be checked Source

Another case is when the device functioning on nickel-cadmium batteries is broken. These batteries are the most common and can be reconditioned in two ways:

The essence of the method boils down to diluting the electrolyte in the can. To be used when most of the substance is retained in the jar, but decreases in volume. The procedure is performed according to the following scheme:

  • A small hole is made in the end part of the jar next to the “-” contact.
  • Using a syringe, about 1 ml of air is pumped out through it.
  • Then 0.5 to 1 ml of distilled water is injected through it with a syringe.
  • The hole is then sealed with, for example, epoxy resin.

Further all batteries were subjected to 5 times full charge-discharge, in order to restore the serviceability.

The procedure consists of applying more current to the banks of the electric screwdriver battery than the value of the rating requires. which eliminates the memory effect, increases the reduced capacity, and temporarily avoids replacing them. But in future such battery will need to be renewed all the same.

In addition, if the main reason for the loss of capacity. evaporation of electrolyte, and at the time of the manifestation of the fault it remains critically small, then the method of flashing also will not help to restore performance. Full replacement will be required.

Replacing the old Ni-Mh battery of an electric screwdriver with Li-Ion cells

A detailed description of the procedure for replacing the Ni-Mh cells in the battery of an old electric screwdriver with Li-Ion cells. Particular attention is paid to the process of selecting components.

How much will it cost to replace the old nickel batteries with lithium-ion batteries in my electric screwdriver?”.This is probably one of the most popular questions you hear from our customers. And indeed, the problem is quite common. Many people have an old cordless electric screwdriver (wrench, peorator, jigsaw, grass trimmer, etc.д.This is a first, and foremost, main thing is that Li-Ion batteries have much higher electric density than Ni-Mh batteries, but the main thing is that these batteries have much higher electric density than Ni-Mh batteries, which means that the batteries are used without any help from the manufacturer (for this reason the Ni-Mh batteries are much more often used with an outdated technology).

There are really many reasons for this desire:. The first and the foremost is that Li-Ion batteries have a much higher electrical density than Ni-Mh batteries. Simply put, for the same weight, a Li-Ion battery will have more electrical capacity than a Ni-Mh. That’s why we get a much longer working time when we put the lithium-ion batteries into the old machine.

But there are enough stopping factors for such an idea:. Because of technological limitations, Li-Ion batteries cannot be charged over 4.25-4.35V and discharged below 2.5-2.7V (indicated in the technical specifications for each particular battery). If these values are exceeded, you can damage the battery and damage it. Special charge-discharge controllers are used to protect the Li-Ion battery, which keep the voltage on the Li-Ion cell within the allowed limits. Т.e besides the batteries themselves you also need a charge-discharge controller The voltage of Li-ion batteries is always a multiple of 3.7V (3.6V), while that of Ni-Mh batteries is a multiple of 1.2V. This is due to the nominal voltage (the amount of voltage that holds on the Li-Ion battery for a long enough time in the middle of the volt-ampere characteristic of the discharge curve) on a single cell. For Li-ion batteries, this voltage is 3.7V, for Ni-Mh. 1,2В. So you can never assemble a 12V battery from Li-Ion batteries. Nominally, it can be 11.1V (3 in series) or 14.8V (4 in series). over, the voltage of the Li-Ion cell varies during operation from fully charged- 4.25V to fully discharged.2,5В. Thus the voltage of 3S. 3 in series) battery pack will vary in voltage from 12.6V (4.2×3) to 7.5В (2.5х3). For 4S battery. 16.8V to 10V Li-Ion battery 18650, and 99 percent of all Li-Ion batteries consist of 18650 cells, has excellent dimensions as compared to the Ni-Mh cell. The 18650 has an overall diameter of 18 mm and a height of 65 mm. It is important to “estimate” how many Li-Ion cells you can fit in your battery case. It should be understood that for the 11.1V battery you need a multiple of 3 Li-ion cells. For the 14.8V battery. four. The charger (charger) for Li-Ion batteries is different from the charger for Ni-Mh batteries. For the sake of fairness, it should be noted that chargers supplied with many impact wrenches are universal chargers and can charge both NI-Cd, Ni-Mh and Li-ion batteries. Make sure your charger has this capability Cost of Li-ion batteries. compared to Ni-Mh batteries can differ many times over.

batteries, electric, screwdriver, lithium

If all of the above does not scare you, then consider an example of the process of manufacturing a Li-Ion battery to replace our existing Ni-Mh battery from the wrench DeWALT DC840.

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This impact wrench comes with two 12V Ni-Mh batteries with a capacity of 2.6Ah.

First, we will determine the nominal voltage for our Li-ion battery pack.

The choice is between a 3S Li-Ion battery with a voltage range of 12.6V. 7.5V or a 4S Li-Ion battery with a voltage range of 16.8V. 10В. We’ll go with the second option because: a) the battery voltage drops fairly quickly from maximum to nominal, t.е. from 16.8V to 14.8V, and for the electric motor, which in fact is the wrench, an excess of 2.8V is not critical. b) The minimum voltage of a 3S Li-Ion battery is 7.5V, which is extremely low for a power tool to work properly. And the efficiency of the 4S battery in this case will be higher than the efficiency of the 3S Li-Ion battery. c) By installing 4 Li-ion cells we will increase the electrical capacity of our battery.

So, with the first point solved: we do 4S (14.8V) Li-Ion battery.

Second. Decide on the choice of Li-ion cells.

For this we have to determine the limiting factors. In the case of making a Li-Ion battery for power tools, the main limitation is the maximum load current. Nowadays there are Li-Ion batteries with allowable nominal (continuous) load current of 20-25A. Impulse (short-term, up to 1-2 seconds) values of load current can reach 30-35A. You will not break the structure of the battery.

Up to 6 Li-Ion 18650 cells can comfortably fit into our housing from an old Ni-Mh battery. So we cannot build a 4S2P (4 in series and 2 in parallel) Li-ion battery for which we need 8 cells and we have to fit in 4 cells. Of course, in this case, each of the cells must “hold” a single value of maximum load current over the entire range of the power tool.

What are the challenges of upgrading?

Before you start, you must determine the feasibility of the retrofit. It is more reasonable not to remake low-quality or long-used tools. it is unprofitable.

The cost of materials and effort is 2/3 the cost of the equipment.It is more reasonable to buy a new electric screwdriver or drill. There are other things to consider:

  • Lithium battery packs of 18650 standard (only they will fit as a replacement) are 6.5 cm and a diameter of 1.8 cm. Ni-CD socket is not suitable for Li-ion. Batteries must be installed in the battery case. You have to install wires and protective circuit by yourself.
  • Li-ion output voltage is 3.6 В. Ni-CD batteries have a diameter of 1 cm.2 В. New batteries may simply be incompatible with the equipment.
  • Li-ion batteries will not withstand a recharge voltage greater than 4.2V and discharge to 2.7 В. Working in this mode will very quickly destroy the battery cells, so the installation of a protection board is mandatory.
  • The native charger (included with the equipment to run on Ni-CD) in 8 out of 10 cases can not be used for Li-ion. Will need to buy new. If there are no plans to buy, then you must also remake the charger of an electric screwdriver to work from lithium batteries, which also can have its own difficulties.

Redesigning the tool does not exclude all the inconveniences.

New lithium battery exhibits poor performance at low temperatures. Must weigh the pros and cons when starting out.

Pros and cons of upgrading an electric screwdriver

One minus has already been indicated. the rapid decline in cell capacity at ambient temperatures below 7-100C. There is another. the price of batteries, but unlike Ni-CD cells, lithium-ion batteries are much more durable. Ni-Cd batteries are chemically unpredictable. If one battery fails, the remaining batteries will not provide the necessary voltage to operate the equipment.

  • The capacity of lithium-ion batteries is twice as much as nickel-cadmium batteries of the same parameters;
  • No “memory effect” of the charge. Charging can be done at any discharge of the cell, at any time.
  • The 18650 standard will lighten the weight of the design. It will be easier and easier to work.

Do not forget about the need to install the protection board (overheating Li-ion cell explodes, can provoke a fire) in the course of work.

Pros and cons of retrofitting

Before how to convert an electric screwdriver to lithium batteries 18650, it is necessary to understand what the master will get as a result. The advantages of these manipulations are as follows:

  • multiple times longer operating time of the electric screwdriver;
  • Increase the speed of charge of the battery. for a full set of energy for lithium batteries you need approximately 1 hour;
  • Increase the charging current to a value of 1-2 C;
  • Reducing the cost of regular purchase of new NiCd batteries due to their insufficient service life;
  • complete absence of memory effect in lithium batteries.

Also, before you remake the battery with your own hands for a more modern technology, you should be aware of the negative consequences:

  • a battery charge controller must be connected to determine the level of charge, as the device must not be charged over 4.2 V and discharged under 2.7 V;
  • Li-Ion batteries for the Li-Lon series of screwdrivers lose their abilities when operated at low temperatures;
  • when converting an electric screwdriver to a lithium battery, you may have difficulty adapting the charger from NiCd, here you will have to use a universal device.

Power supply for charging

Warning ! The Li-ion assembly must be charged strictly with a battery charger for lithium batteries! The charger for nickel will not work! To buy the right charging unit, you need to multiply the number of batteries in your assembly by 4.2. Т.е. 1х188650. 4.2v, 2. 8.4v, 3- 12.6v and so on. There are a lot of different power supplies on aliexpress, just type power supply 4 into your search.2v (or whatever voltage you need)

Silicone wire

Of course you also need a wire. And, to be blunt, a good piece of good, soft silicone wire will come in handy even without remodeling or repairing your electric screwdriver.

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Well, there you have it. At aliexpress there is absolutely everything you may need to replace your old 18650 batteries with new ones in your electric screwdriver or to switch your electric screwdriver from nickel to lithium-ion batteries.

By the way, you can buy a lot of good cordless tools (selection one and two) and screwdriver attachments there on aliexpress.

If you work with an electric screwdriver or any other tool, you will probably need a good headlamp. Now on aliexpress there is an opportunity to buy really inexpensive and good model: with built-in charging, good for brightness and color temperature light, a magnet in the end (ideal for work under the hood). If you’re interested, here’s my full review and comparison of the Sofirn SP40

Well and below, in the “about the author” section there are many other useful picks.

Advantages of the second option

The second option is more suitable, because the voltage in the battery rather quickly falls from the maximum to the minimum (from 16.8 to 14.8 V). For an electric motor, which, in fact, an electric screwdriver is not, an excess of 3.5.8 V is not critical.

The 3S-Li-Ion modification has the lowest voltage rating. It is equal to 7.5 V, which is insufficient for the production activity of the electrical device. By assembling the four configurations, we will increase the electrical capacity of the battery.

Technology for replacing Ni-Cd with Li-ion in an electric screwdriver

Lithium cells are characterized by durability, so many screwdriver owners think about replacing nickel-cadmium products with them.

Replacement technology includes several steps that must be followed.

Determining the number of Li-ion batteries

Basically, the parameters of the battery are marked on the battery itself or on the electric screwdriver. To determine the number of cells required, you need to divide the voltage indicated on the tool by 1.2V (this is the nominal voltage of one nickel bank).

To find out how much lithium parts you need to replace, you divide by 3.7 V, which is the normal value for this type of battery.

It is recommended to round up the obtained result, it will not have a negative impact on the tool, but simply increase its power a little.

Requires correct selection of all necessary elements for replacement

Choosing a Li-ion battery

Lithium-ion and lithium-polymer cells are available from manufacturers. The latter are smaller and safer, but also cost more. At the same time, they are not able to deliver high currents. Therefore, experts recommend taking ordinary lithium-ion banks.

It is better if the element has welded flexible taps, because such parts do not like high temperatures and unnecessary soldering. It is recommended to look at several options in stores to choose the most suitable model.

How the value of the battery voltage affects the operating time of an electric screwdriver

The question of how battery voltage affects how long the product lasts is of interest to many. To understand what power a product has, you need to multiply the voltage by the battery capacity.

For your reference! For example, an electric screwdriver with a 14.4 V battery and a capacity of 1.5 A / h will have a capacity of 21.6 W.

Prefabricated 18650 battery packs

It is better to buy prefabricated assemblies of 18650 batteries as a substitute. You can do it on Chinese online marketplaces or other online stores.

Selecting the BMS protection board

Lithium-ion batteries require care and adherence to certain requirements. The BMS board performs the role of protection. This particular cell does not allow the battery voltage to exceed 4.2V or drop below 2.55V per battery while charging. In addition, the cell keeps the maximum allowable current under control and maintains the necessary balance between the batteries.

The main parameters when choosing are the number of cells connected in series. On the Internet you can see a table with all the necessary parameters and use it to select the appropriate board.

You can even do the replacement at home, the main thing is to follow the sequence

Power supply for charging

For lithium-ion batteries, the chargers are chosen based on the number of batteries in series in the battery. The more there are, the higher the output voltage should be.

Charging the batteries with a regular charger from an electric screwdriver

If you want, you can buy a special universal board for the lithium battery. It is installed in the native charger. However, experts recommend using suitable chargers for this type of battery, rather than refinements.

Lithium Battery Capacity Indicator

Indicators are LED and digital. The latter are cheaper, but not convenient to use. It is better to choose LED versions based on the number of batteries in series.

18650 battery holder

It is also better to buy ready made holders for 18650 batteries. If you want, you can find good options at affordable in online stores.

Elimination of memory effect

It is not always necessary to perform radical actions to recover a screwdriver battery. It often helps to restore the capacity of the battery by alternating between full charging (until the charging lamp goes out) and full discharging of the battery. This method is also called “rocking the battery”.

How to erase the memory effect of the battery

It is connected with the so-called “memory effect” and is characteristic of nickel-based screwdriver batteries. This is especially apparent in nickel cadmium batteries. It occurs when the battery, discharged to zero, is not fully charged and begins to operate, or vice versa. This leads to enlargement of the active substance crystals, which reduces the active surface area of the battery.

Follow the manufacturer’s recommendations for charging and discharging modes.

A so called “training” of the battery helps to remove or significantly reduce this effect. It consists of repeating cycles of full charge and discharge.

To do this the battery to be restored is completely discharged, for example, using a light bulb. Then the battery is fully charged and discharged again. Repeat the process 5 times and if the individual elements of the battery are intact, the characteristics will return to normal or close to it.


Failure of power units occurs when screwdrivers are often used as a drill. Active overloading can cause the electrolyte inside the batteries to boil. This is fraught with bloating of their casings and leakage of electrolyte.

To avoid spending too much money for a new battery, it’s important to check the battery’s condition. It can only be done by repairing the charging cells. The battery is checked in this order:

  • Connect the battery to the charger.
  • Measure the voltage after half an hour. The voltage value is usually 13 volts. After 2 hours the voltage at the battery terminals is 14 volts. Your battery will finally show 17v.
  • If the battery has a current of 1A or more after 60 minutes of charging, it is in good condition.
  • Next, check the battery under load. Usually connect a 40 watt bulb or take a 12 volt, 35 watt car headlamp bulb.
  • If, after three minutes, the voltage across the battery terminals is less than 12.4 volts, one of the batteries, or several at once, needs to be replaced.

Measuring the battery voltage