How to fix an electric screwdriver battery. Choosing which parts to replace

Electric screwdriver battery recovery, rebuilding and repair

It is no secret that the cost of a new battery for an electric screwdriver is equal to 70% of the entire cost of the apparatus. In the process of operation, any rechargeable battery (ACB) begins to lose its capacity and as a result completely or partially fails. But you should not throw away the battery that has reached the end of its life, because it can be reanimated at home.

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The main faults of an electric screwdriver battery include the following:

Electric screwdriver battery failure can be caused by the failure of one or more storage cells. Failure of all the jars in the battery pack is very rare, so it is quite possible to repair the battery. Since all the banks are connected in series, you will need to disassemble the unit and find the faulty.

A complete check of the battery is carried out in several steps, with a fully charged battery.

Checking with a multimeter

Since all components of the battery pack must have the same voltage level, it is not difficult to find the faulty cell. A multimeter is usually used for this purpose, switching it to voltage measurement mode. When measuring, you should consider the nominal voltage for the different types of batteries:

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  • Li-Ion (lithium-ion) battery has a nominal voltage of 3.6-3.8 V;
  • Ni-Cd (nickel cadmium) and Ni-MH (nickel metal hydride) batteries are rated at 1.2-1.4 V.

Finding a faulty battery is as follows.

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  • You need to recharge the battery and wait for it to be fully charged.
  • Disassemble the battery housing, remove all the banks and measure the voltage at each one.
  • The banks with a voltage rating below the standard voltage should be marked.
  • Assemble the battery pack with all the cells taken out and connect it to the screwdriver.
  • In the next step, it is necessary to turn on the tool and perform several operations with it to achieve a noticeable drop in power.
  • After discharging, you should again disassemble the battery pack and make voltage measurements on all batteries in the circuit. Pay special attention to the marked banks.
  • If you notice a voltage drop of 0.5-0.7 V on any of the cells, then such a battery can be considered unsuitable, and it will have to be replaced.

Load test

To find out how long it takes to fully drain the battery, you need to check the battery under load. The latter is selected according to the capacity of the battery.

Generally it is recommended that the load for testing the battery should be between 35-40 watts. A 12-volt light bulb with 40 watts of power can be used for this.

Connect a battery through an ammeter to a light bulb for 2-3 minutes. All measurements should be made with a voltmeter. Voltage at battery outputs must be slightly over 12.4 V. If the reading has dropped during this time and is in the 12-12.4 V range, it indicates that there are faulty banks in the circuit. Also the fact that there are defective elements in the unit can be signaled by the drop in brightness of the connected lamp.

Types of batteries used in screwdrivers and their differences

Battery-powered tools use nickel- or lithium-based power sources. The bank is equipped with a moisture-proof case made of impact-resistant plastic, inside there are cells connected in a common circuit.

On the lid of the bank there is a guide tab with contact pads designed for charging and connecting the battery to the tool. Design includes plastic locks to prevent spontaneous battery separation during operation.

Nickel-metal hydride batteries

Characterized by an increased density of stored energy, but the value of the maximum current in the circuit is inferior to that of cadmium batteries. The products have a low rate of self-discharge, during normal operation there is a slight decrease in voltage. The materials used in construction are environmentally friendly, and to restore the battery the current of no more than 30% of its nominal capacity is required.


These cells are most often used to drive tool motors. Each section has an operating voltage of 1.2 V, and the parts are assembled into common banks.

The advantage of batteries is the ability to supply higher rated current, but there is a capacitance drop when the battery is partially discharged.

The process is reversible, and successive periods of discharging and charging are required for recovery. Cadmium power supply lasts up to 1,000 cycles.


Characterized by reduced self-discharge and increased capacity (without increasing the size). No maintenance is required during operation. Special devices are used for charging, because if the procedure is not followed, the element can ignite or explode. Mechanical defects negatively affect the stability of the battery, which crashes or ignites when attempting to charge.

Lithium-ion batteries are equipped with safety mechanisms, which are triggered at the moment of high-current discharge. An anode made of graphite has been introduced into the design to reduce the probability of explosion.

But the tendency to spontaneous ignition when storage and operating conditions are not met is still present. Power sources do not tolerate deep discharge, increasing the voltage in the charging circuit leads to an irreversible loss of capacity.

Black and Decker KC9072 Screwdriver Battery Replacement

Lithium Polymer

But batteries retain a high fire hazard if used improperly. The design of the bank has an electronic protection circuit board that limits the maximum current in the circuit. To restore the capacity you need to use a special charger, the power supply can withstand up to 900 operating cycles.

Deep discharges must not be allowed, the product fails in case of prolonged storage. To reduce natural wear and tear, special inhibitors are added to the electrolyte.

What kind of batteries are in a screwdriver

The screwdrivers can be equipped with nickel-cadmium, nickel-metal hydride or lithium-ion batteries. As a rule, in more modern models are installed lithium-ion batteries.

These batteries are the best option for use in screwdrivers for their combination of characteristics:

But along with the advantages there are significant disadvantages. significant temperature limitations. Operation is not possible at low temperatures, because the battery discharges quickly, threatening to self-ignite or explode under a sudden impact or if it heats up too much.

The differences between nickel-cadmium and lithium-ion batteries:

  • have a lower capacity;
  • more weight;
  • not so afraid of frost;
  • the electrolyte dries out when reaching the end of its service life;
  • there is a “memory effect”. The capacity of the battery can decrease dramatically as a result of improper use, when not fully discharged battery is put on charge.

Nickel-metal hydride batteries compared to lithium-ion batteries have:

Batteries of this type cannot be restored at the end of their service life.

In principle, the construction of the battery itself does not depend on the type of batteries. The only difference will be in their number, since the voltage of a single lithium-ion cell is 3.6 to 3.8 V. The voltage of a single nickel-cadmium battery cell is 1.2 to 1.4 V.

In addition to the batteries, the battery case has a protection and control circuit, a temperature sensor and a contact block.

How to eliminate the memory effect

If the battery is repeatedly put into insufficient charge and then discharged, it develops a so-called memory effect. That is, the battery gradually as if to remember the minimum limit of charging and discharging, as a result, its capacity is not fully used and gradually decreases still and more.

This problem is most common with nickel-cadmium batteries and is less prevalent with nickel-metal hydride batteries. In any case it is necessary to restore the capacity of the battery. The memory effect does not apply to lithium-ion batteries at all. To solve the problem of whether the cell can be repaired, it is recommended to perform a complete discharge and charging of the battery with a 12 volt light bulb. The plus and minus wires are soldered to it and connected to the battery terminals. This procedure is repeated five times or more.

Restoring with distilled water. truth or fiction?

Many craftsmen capable of restoring power tools claim that dried out power sources do not lend themselves to “reincarnation”. Others say that batteries can be restored, all you need is distilled water, a tool and 30-40 minutes of free time.

Battery recovery sequence with distilled water:

  • Using a thin drill bit and a drill, make a small hole in the top of the battery bank. If you drill into the middle or bottom of the cell, you could damage the power supply. It will not be possible to repair it later.
  • Using a syringe pour distilled water into the battery up to the maximum.
  • Leave the battery in a clean and warm place for 1-2 days, without covering the opening.
  • Cells with poured distilled water connect into one battery.
  • Place the battery on charge until the capacity is fully restored. After charging, check the voltage on each jar and top up with distilled water if necessary.
  • After checking, close the holes with a glue gun. Never tamp the holes. it may damage the battery cell.
  • Put the battery back in its case, close the lid and recharge.

The home method with the electrolyte works, but not always. Sometimes the internal structure of the battery is so damaged that even distilled water does not give a positive result.

Repairing the battery by replacing several elements

Restoring the battery of an electric screwdriver by replacing several cells can be successful for all types of batteries. It is also no risk for them, as well as the manipulation with distilled water, provided that care is taken during the soldering.

First, using a multimeter, measure the output voltage of each “bank”, which in total should be 12-14 V. Accordingly, the voltage of one “can” should be 1.2-1.4 V. U values are compared with each other, the weakest cells are marked with a felt-tip pen. Read more about how to check the battery of an electric screwdriver with a multimeter

The battery is then inserted into an electric screwdriver and run until the power begins to decrease noticeably. The voltage readings are taken again, and those “banks” whose voltage difference is 0.5-0.7 V compared to the “stronger” ones, should be unsoldered, discarded and replaced with new ones, similar to the old ones, having previously ordered them in an online store.

Soldering the battery chain is recommended by spot welding, but if such is not available, there is nothing to do but to use an ordinary soldering iron and do everything as quickly and clearly as possible, so as to avoid overheating the battery.

The “native” connecting plates of the battery should not be lost, they must be soldered back without reversing the polarity. In addition, all elements in the chain must have the same capacity.

After finishing soldering, insert the battery back into the electric screwdriver and conduct 2-3 cycles of full “charge-discharge” to equalize the energy potential of all batteries. In order for the updated battery to last longer, such a training should be carried out 2-3 times a month. On how to quickly and completely discharge the battery of an electric screwdriver →

Features of types of batteries

The battery is the most important part in an electric screwdriver. If the tool began to work poorly, then one of the reasons is the failure of the battery. A new battery pack costs a little less than the electric screwdriver itself. And you have to make a serious choice. buy a new unit or a new tool. Not a cheap treat.

But, if man made it, man can also repair. The main thing is that the head works and the hands have the right source. With their own hands you can do battery repair, which after that will work for more than one year.

Batteries are composed of several elements. They are very similar to conventional batteries, but can be recharged. The number of charge cycles determines the main price of cells. According to the type of material, battery cells are divided into:

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In the list they are arranged by frequency of use. Nickel-cadmium cells (Ni-Cd) are the most common in screwdrivers of various brands. This is due to their comparative cheapness. But they have a low voltage output and the number of charge-discharge cycles is also low. The voltage of one such battery is about 1 V.2 В. If the screwdriver requires 12 V to work, the battery must consist of at least 12 of these cells.

They can be stored uncharged for a long time and are not afraid of temperatures. But the level of self-discharge forces the battery to charge frequently, which is the reason for failure. The ecology of the production of such batteries is not acceptable in every country of the world, but maybe that is why they are cheaper.

Lithium-ion (Li. Ion) batteries have the best performance. Voltage on an individual instance reaches 3.6 В. High capacity charge. Four pieces are enough for the tool to work. It’s a joy to handle, because the tool has to be both carried and held at any height. Number of charge cycles is high, but the price is not low either. But the battery has no “memory” of the charge level. And the self-discharge is small. In short, everything is good except the price.

Nickel-metal hydride (Ni-MH) batteries have almost all the shortcomings of the previous brands. With the quality of nickel-cadmium cells their price is equal to that of lithium-ion cells. Application in practice is very low where there are low temperatures. Low temperatures put the whole battery out of action at once.

It is possible to repair a battery with your own hands, but that does not mean that you can repair a single cell. One cell can try to be restored, and if restoration does not help, it must simply be replaced. All battery cells can be replaced. This is the best option. buy new cells and make a replacement. But it’s not always fast, and you need the tool now.

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In fact, what did you do.1) you took originally not intended for a power tool elements. 20a lithium is needed. Your cells give a current of 4.4a when new, things are worse now. Т.е. the screwdriver is blunt and the cells are working at the limit and the fuse in the cells will either blow.2) the charger should give the assembly 12.6v, if more than that, either the fuse will fail or explode.3) if your charger gives the right voltage, remember that without balancer, cells will have completely different voltage, which on discharge will threaten the degradation of the weakest in capacity cells and further failure. And when charging, it is possible to overcharge some cells above 4.2c, which would lead to their death by breaking the safety plates or exploding.Yes, this assembly will work, but not for long and is sure to bring to mind the saying.”The miser pays twice”.Buying 3 elents, new, power and protection board is not that expensive, but will provide safety and many years of flawless operation.

Replacement of all battery pack cells

The right number of cells can be ordered at any online store, depending on the number of old batteries. It is important to pay attention to the fact that they are all initially the same capacity.

You can replace all cells of the battery pack with new Ni-Cd batteries. They are much cheaper than nickel-metal hydride batteries and, compared to other batteries, the most durable and enduring. Recently, however, it has become increasingly common to convert batteries “from cadmium to lithium” on their own, in other words, to install new lithium-ion batteries instead of the old Ni-Cd.

Despite their reliability, nickel-cadmium batteries can fail quickly because they are connected in series with each other without a balancing board. If the batteries are of the same batch manufacture, their parameters will still have a large variation between each other. With this connection, one cell will charge faster, the other slower, and the third may also overcharge.

If cadmium battery makers made balancing boards like they do for lithium batteries, Ni-Cd could last much longer. But this is simply not profitable for the manufacturing companies. As for lithium cells, balancing boards are installed in such battery packs because without them overheating can occur with a subsequent explosion: there is simply nowhere for the manufacturers to go. To find out which battery is best for an electric screwdriver, click here →

To make a complete replacement of the batteries in an electric screwdriver from nickel-cadmium to lithium-ion, you will need:

How to Repair Electric Screwdriver

  • the number of elements equal to the number of former (with the same capacity value);
  • 5S balancing board (its amperage depends on how many volts the electric screwdriver is designed for);
  • tester or multimeter ;
  • a soldering iron with a good tip;
  • Use good quality flux and lead solder;
  • silicone wire AVG 16 ;
  • Heat-resistant adhesive tape and hot melt glue.

Discharge batteries before starting soldering. Remove the old batteries from the block and free the contacts. It is better not to throw out the old temperature sensor, but to keep it as an additional protection against lithium overheating.

Now the most important thing is to solder lithium properly. Cut in advance the wires of the right length, insulated, in silicone, very thick, to avoid their melting when heating the lithium. Use a knife to deburr the solder pads of the batteries.

Heat up the iron to 300°C and start soldering with flux and lead solder. Flux must be of good quality, indelible, non-conductive. Never use acid fluxes. Do not solder for more than 2 seconds to avoid overheating the lithium. To ensure that the heat escapes faster, you can, after soldering, put to the battery any iron object that takes the heat.

Allow the batteries to cool and connect the pluses and minuses as usual. Check the total voltage. Its indicator should be on average 20.7 V if the cells are 15 pieces.

After measuring the voltage, connect the board. All its wires should be laid with special pads so that nothing gets “shorted” during operation. Secure the entire battery pack with heat-resistant adhesive tape designed specifically to insulate the batteries and their contacts.

Solder wires and connector. If the contacts are “loose”, they can be sealed with hot melt. Now, finally, you can assemble the battery pack of your electric screwdriver and test its functionality.

Sometimes it seems very difficult to repair the battery of a Hitachi electric screwdriver (or other tool). But if you understand the general principles, such as the basics of electronics, the construction of batteries from the inside, types of batteries and the main principles of proper soldering, it becomes clear how to repair the battery for an electric screwdriver yourself. This will not only save money, but also contribute to the acquisition of valuable and useful skills.