Can an electric screwdriver battery be repaired?

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How to repair an electric screwdriver battery and its malfunctions

Cordless electric screwdriver, can always come in handy in the household, but over time, its power source suddenly refuses to work. It is expensive to buy a new electric screwdriver. Its price is about 70% of the cost of the battery. And because models change frequently, it is difficult to find a new battery for this particular tool. That raises the question of what to do next. Buy an electric screwdriver or look for a similar battery? But this problem can be solved by repairing the battery itself, prolonging its life for a few more years.

It is worth noting that batteries for almost all brands of screwdrivers, regardless of what country they are manufactured in, have a similar design. But each type of battery has its own particular characteristics.

If you take a battery apart, you’ll see that it’s made up of separate cells connected in a common circuit in series. Many people should remember from their school years that charging cells connected in series in one electrical circuit increases the total capacity.

Battery types

Has a fairly high capacity, so one full charge can be enough for 1500 operating cycles. But it needs constant charging. Also this type of batteries is not recommended for low temperatures.

Practically the cheapest batteries with a rated voltage of 12.5 V. They have a small capacity, so the discharge occurs rather quickly. But they can’t be recharged. So in order to prolong the life of these batteries, it is recommended to fully discharge them before charging. The advantage of nickel-cadmium batteries is that they recharge quickly, can be used for quite a long time with proper maintenance and work well at low temperatures.

They have a high capacity, recharge quickly. It is possible to recharge the battery freely at any period of time, but it must not be allowed to be completely discharged. Also not recommended for use at low temperatures. Do not tolerate long storage periods without periodic discharging and recharging (after a certain period of storage it is recommended to load the battery).

There are two contacts on the battery case marked plus/minus for power to the electric screwdriver and 2 contacts for charging. A thermistor is connected to one of the charging contacts to protect the battery from overheating during charging. The thermistor completely shuts off or reduces the charging current when the batteries reach a temperature of 50-60 degrees. Batteries often overheat during intensive, so called “fast” charging.

Causes of malfunction

Battery failure is possible for a variety of reasons. Therefore, before you try to repair it, you should make sure that this action is worthwhile. It may happen that the labor intensity and the cost of its repair will be more expensive than a new purchase.

For example, a frequent source of problems that cause the battery to stop working is its long life. In some types of batteries, after a certain period of time, the capacity of the batteries decreases, and they quickly discharge during operation. Naturally, in this case, you probably can not restore their performance.

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There are also some other malfunctions:

Eliminating the memory effect

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

How to erase the memory effect of the battery

This is caused by the so-called “memory effect” and is characteristic of nickel batteries. And it is especially strong in nickel-cadmium. It occurs when the battery is not fully charged and begins to run or vice versa. It causes the crystals of the active substance to enlarge, which reduces its active surface area.

Follow the manufacturer’s recommendations for charging and discharging.

A so-called “conditioning” of the battery helps to eliminate or significantly reduce this effect. It consists in repeating the full charge and discharge cycle.

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

Design features of the battery pack

Regardless of the brand of power tool and its specifications, the design of batteries is almost identical. If you disassemble the battery, you can see that it consists of identical batteries assembled in a series electrical circuit.

And for all kinds of cells, having almost the same size and voltage rating, they may differ in capacity (indicated on the case). If the repair is carried out independently it is necessary to pay attention to the type of batteries used, because the recovery technique for each type may be different.

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To connect the device to the mains and make its charging, the design provides power contacts, which are connected to the pins of the circuit. There are two more control contacts on the battery case, to which resistors and thermistor are connected. From these parts assembled a system to protect the equipment from overheating during charging and leveling the necessary charge at each can of battery.

How to repair an electric screwdriver battery

Algorithm of restoration of DC power source for electric tool depends on the chemical composition of the sections. For example, the water refilling procedure is used for nickel-cadmium products. Repairing lithium batteries requires replacing the failed sections.

In factory conditions the contact plates are connected by jumpers, fixed by welding. Repair at home is carried out by soldering with special fluxes.

Bleeding the gas from the battery

During the operation of lithium-ion cells, gases are produced which raise the pressure inside the case. If the design does not provide for a drain valve, there is a deformation of the housing wall and cover. On some products, the bloated case opens the contacts of the protective fuse, reducing the voltage at the terminals to zero. The defective element is identified with a testing device and then removed from the can.

Place the battery on a hard surface, using a suitable tool, press the swollen plate into place. Gas escapes from the body cavity through the slots formed, but later the section fails due to leakage and evaporation of electrolyte through the hole.

The second method of restoration is devoid of such a disadvantage, the method is based on a forced bleeding of gas.

The positive contact plate is bent sideways, then a blunted awl is used to tap the safety plate out of its original position on the body. A hole is made in the cover and the excess gas is bled out through it (you can hear it hissing). Then the blown cap is pressed into place, and the hole is filled with solder or silicone sealant. Positive plate is attached additionally.

Repair with water

One common technique for recovering nickel-cadmium cells is to add distilled water to the cans (using tap or boiled water is strictly prohibited).

The procedure does not require any special tools and can be performed with your own hands at home.

The user has to take apart the plastic cover of the battery and remove the cylindrical elements installed inside.

Then with the help of test device is defined the parts with minimum voltage (1 V and below).

The addition of distilled water is made with a clean medical syringe through a hole in the housing with a diameter of no more than 1 mm. The needle is cut to a length of 1-1.5 mm and then the tip is inserted into the cover. 0.7-1.0 cm³ of liquid is poured into the inside of the jar, with additional refilling up to 0.5 cm³ (the data given are for a 18650 standard cell).

By replacing several elements

To restore the performance of the bank it is possible to replace the defective batteries. To determine the damaged nodes, a test instrument is used, the measurement is made after removing the protective plastic cover.

Batteries with a voltage lower than 0.7 V (for the nickel-cadmium version) and less than 2.5 V (for the lithium-ion version) should be discarded. These products are replaced by batteries with identical dimensions and parameters, the jumpers are soldered with tin-lead solder (using special flux or rosin).

How to eliminate the memory effect

If not fully charged and then discharged, there is a reversible decrease in battery capacity, called the memory effect. The device remembers the lower limit of the values, which leads to a gradual deterioration of the performance. The phenomenon is noticeable on nickel cadmium type products, nickel metal hydride batteries have a weak memory effect. Lithium-ion devices are not subject to this effect.

To restore the capacity you need to fully discharge the power supply with an incandescent lamp (designed for 12 volts) and then connect the regular charger. The procedure is repeated 3 to 5 times to bring the capacity up to the starting value.

How to refill with distilled water

Sequence of operations when filling the battery with water:

  • Separate defective cells from the common battery bank, jumpers are stored for later reassembly.
  • Drill the side surface of the casing at the bend in the wall. Drill down to the thickness of the casing material, but do not allow the drill bit to penetrate the electrolyte.
  • put 1 ml of distilled water into the battery cavity (with a medical syringe with a shortened needle).
  • Let the battery stand at room temperature for 24 hours, then take a voltage reading.
  • Charge the battery with a device designed for nickel-cadmium power sources.
  • Keep the battery for 5-7 days and then check the voltage. If the reading has dropped, then an additional dose of water is poured and the battery is recharged. If the parameters have not dropped, then seal the case (with solder or silicone material).
  • Connect the batteries in a common bank, using contact welding or soldering. Conduct practice cycles of discharging and charging the battery to increase capacity.

The method is only suitable for nickel-cadmium type products, other batteries can not be charged with water.

Where to buy lithium batteries to replace defective ones?

And finally, let’s talk about lithium battery replacement. If it happens that the batteries in your screwdriver have fallen into disrepair and it is necessary to replace them, then at the moment it is not difficult to find a decent replacement. For example, you can find lithium batteries from Samsung, LG, Sanyo, Panasonic, Sony on AliExpress.

To upgrade my 12V screwdriver with nickel-cadmium battery, I bought Samsung INR18650-25RM batteries.

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I bought it in the well known and trusted LiitoKala store. Apparently, the batteries are original. Anyway, the difference in weight, capacity, workmanship I have not noticed. The seller bluntly writes that the batteries are original, but they apparently do not have the right to “shine” brand Samsung. That’s why all batteries have Samsung branding plastered with a store sticker.

Conversion successful. I did not bother with protection and charging cards, I just brought out the power leads, as well as wires for the balancing connector. I charge everything directly from a Turnigy Accucell 6 universal charger. I was just hustling because the summer was coming to an end.

To replace nickel (NiCd, NiMh) batteries with lithium it is better to take those with welded “petals”. This makes it easier to solder the composite battery.

It is worth noting that the batteries INR18650-25RM just the same and are used in those “Pack for Power Tool” for power tools. Before buying the battery I advise you to google the datasheet for the battery (for example: “Samsung inr18650-25rm datasheet”). It contains everything you need to know: typical charge and discharge currents, purpose (tools, toys), graphs of capacity loss after several cycles and much more.

What is the problem when using Ni─Cd batteries?

During the operation of Ni─Cd batteries the voltage and the discharge capacity are gradually reduced. Below are the main factors that cause these processes:

  • reduction of the working surface of positive and negative electrodes;
  • loss of active mass, as well as its redistribution over the electrodes;
  • the occurrence of current leakage due to the formation of dendrites of metallic Cd;
  • processes that result in irreversible consumption of water and oxygen;
  • changing the composition and volume of the electrolyte.

similar processes occur when operating Ni-MH batteries. The only difference is in the electrode materials used.

During the operation of Ni─Cd batteries, due to the redistribution of the active mass over the electrodes, the mechanical strength and volume of the nickel-oxide (positive) electrode change. As a result, the contact between the active mass and the electrode deteriorates. All this causes a decrease of conductivity and a decrease of capacity. In the neglected case the contact between positive and negative electrodes is simply broken. As a result, the battery ceases to show signs of life.

All these changes of the nickel-oxide electrode are caused by permanent overcharging, during which the release of oxygen occurs in the space of the positive electrode. The more batteries go through charge-discharge cycles, the more the crystals of the active mass of the positive electrode become enlarged. Therefore, the working surface decreases, and therefore the capacity of the battery.

At the cadmium electrode, the degradation process is mainly determined by the migration of the active mass. As a result, there is some loss of it. In addition, the active mass clogs the pores in the surface layer of the negative electrode. This makes it difficult for the electrolyte to reach the deeper layers. The result of active mass migration is the growth of dendritic bridges through the separator to the positive electrode. This leads to numerous microcircuits and increases self-discharge. The cadmium electrode also has a growth of crystals and an increase in the volume of the active mass.

In addition to the processes described above, in Ni─Cd batteries the oxidation of the various additives present in the battery takes place. The metalloceramics of the positive electrode gradually oxidize with the consumption of water. And one more unpleasant process which leads to loss of serviceability of Ni─Cd battery is a withdrawal of electrolyte from the separator. This is due to a change in the porous structure of the electrodes and leads to an increase in the internal resistance of the NiCd battery. The composition of the electrolyte also changes during operation. In particular, the amount of carbonates grows. Reduced conductivity of the electrolyte and drop of all Ni─Cd battery parameters during discharge. The picture becomes especially noticeable at low temperatures. What to do in such cases?

Full replacement and erase of “memory” of batteries

In rare cases, for example, if the battery is too old, then all elements fail. Buying a new battery is still more expensive than replacing all the batteries. Therefore it makes sense to order individual power supplies online, solder them into a battery, and then place them in the old case.

There is a little secret to extend the life of new power sources. To do this, it is necessary to remove the factory settings from the banks, which are set by several charge/discharge cycles. Carry out the operation to extend the longevity should be carried out only on new cells, and then charge them properly.

A new battery pack is discharged to 1 V. It is important to monitor this parameter, because below one volt the battery may become unusable, after which its recovery will be impossible. To discharge it is best to use an adjustable load on which to set a current of 1 A.

After a complete discharge, all elements must be recharged, using the rated current and voltage. Once fully charged, you can solder the power sources into a battery and install it on the screwdriver.

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Types of ACB

Nowadays, the screwdriver can be produced with several varieties of batteries:

At the same time, each type is characterized by its own subtleties.


Lithium-ion models boast unsurpassed build quality and maximum service life. In this respect they have no competitors. Due to the lack of memory such batteries are the ideal power source, although they do have one disadvantage: they cannot be used at minus temperatures.

However, with prolonged use, other disadvantages begin to appear. For example, if a battery loses its service life, the lithium decomposes, and unfortunately this reaction cannot be prevented.


Nickel-cadmium batteries on the other hand behave very differently when they run out of capacity. When they near the end of their useful life, they dry out. To restore the former performance is enough to refill them with a special substance. True, such a procedure requires special attention and some effort.

Instead it is much more reasonable to put a section of new rechargeable batteries in the battery. A memory effect is often the cause of damage, which is a huge drawback of nickel cadmium batteries. To solve the problem it is necessary to flash the electric capacity.

Nickel-metal hydride

If we talk about another type of batteries for electric screwdriver. nickel-metal hydride, then such power sources are not subject to restoration after the exhaustion of the working resource. The only solution would be to quickly replace the battery with a new one.

Considering the option of replacing the power source, it will be indispensable for all types of batteries, which the tool is equipped with. It is no secret that these days you can find a wide variety of such products in specialized stores or on online sites. You can buy a good battery at an affordable price, most importantly, you should know what to consider when choosing. However, in that case you will have to do the replacement yourself, and there are several factors to consider.

The first thing to do is to disassemble the battery into small elements and replace the failed “stuffing” with a new one, bought in the store. Then it remains to reassemble the construction in the reverse order. It is this type of repair work will be discussed further in this material, but first let’s talk about the restoration procedure for nickel-cadmium models.

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Repair and replacement of electric screwdriver battery cells

A more effective way to repair batteries for an electric screwdriver. replacement of elements that we have identified as faulty.

To carry out the repair, we need either a battery. “donor”, in which some of the cells are working, or new “banks”. To get them will not be difficult, even on the Internet you can easily find a dozen stores that are willing to send these elements by mail.

Note. When you buy a new element, make sure that its capacity and dimensions coincide with the native elements.

Also we will need a soldering iron, low-corrosive flux (preferably alcohol flux on rosin) and tin. We don’t talk about spot welding, because for a single battery repair there is hardly a need to buy or collect it.

In the replacement itself there is nothing difficult, especially if at least some of the. then there is experience in soldering. In the pictures is shown in detail, cut off defective element and solder a new one in its place.

  • When soldering with a soldering iron, try to solder quickly so that the battery is not heated, t.к. you run the risk of damaging it;
  • If possible connect with native plates, or use copper plates of the same size, it is important because charging currents are big and with wrong section of the connecting wires they will be warm, respectively thermistor protection will be triggered;
  • Under no circumstances mix up the plus and minus sides of the battery. connection in series, so the minus of the previous bank goes to the plus of the new bank, and the minus of the new one. on the plus side of the next.

After soldering new cells, it is necessary to equalize the potentials at the “banks”, because they are different. Charge/discharge cycle: let it charge at night, let it cool down for a day and measure cell voltage. If we have done everything correctly, the picture will be approximately the following: all cells have the same multimeter reading, within 1.3V.

Next proceed to discharging the battery by inserting the battery into the electric screwdriver and loading it “full”. The main thing is to spare the electric screwdriver, otherwise you will have to repair it too. Bring it to a complete discharge. This procedure should be repeated twice more, i.e.е. Charge and fully discharge.

It should be noted that the procedure of erasing the “memory effect” should be carried out every three months. Conducted by analogy with the above training.

Such a not very tricky procedure will prolong the work of your electric screwdriver, at least until it itself will not have to be replaced with a new one

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