Replacing Items in a Cordless Screwdriver Battery

In the arsenal of any good owner, there will probably be a common power tool today in the home. a screwdriver. Its main advantage is mobility. After all, this device works from removable batteries, which makes its use as convenient as possible, since you do not need to connect to an electrical outlet. But what if the battery (battery) of the screwdriver is out of order? Buying a new one will be quite expensive, because its cost in some models reaches 50–70% of the price of the screwdriver itself. It will be much more practical to immediately purchase a new tool, which comes with two batteries. But you can still extend the life of the old screwdriver by repairing a failed battery.

What is a battery screwdriver

In any model of electric screwdrivers, such an important element as a battery looks about the same. It is a plastic box, inside of which up to a dozen (and sometimes more) batteries are placed. They are interconnected in a sequential chain and are arranged in such a way that the terminals of the first and last banks in the circuit are closed to the contacts providing power to the instrument and connecting to the charger.

The battery of any type of screwdriver has a fairly simple design, which can easily be understood by anyone who is at least a little familiar with the basics of electrical engineering. In addition to batteries in the battery housing can be located:

  • a thermistor (thermal sensor) to protect the battery cans from overheating when charging and a thermal interrupter that serves to open the charge circuit when overheating;
  • control controller board (only in lithium-ion battery).

replacement of elements in the screwdriver battery

Lithium-ion batteries run under a special controller

Depending on the type of batteries used, a screwdriver battery can be of the following types:

  • nickel-cadmium, denoted by NiCd symbols and designed for a nominal voltage of 12 V;
  • nickel metal hydride (NiMh) with the same nominal voltage as the elements of the first type (12 V);
  • lithium-ion (Li-Ion), the voltage of which depending on the number of elements used can be from 14.4 to 36 V.

The first type of rechargeable battery (NiCd) is the most common in modern tools, primarily due to their lowest cost. Especially often, batteries based on nickel-cadmium alloy can be found in budget models of screwdrivers. They are not afraid of low temperatures and can be stored in a discharged state without losing their characteristics. Of the disadvantages of such batteries can be noted:

  • a pronounced memory effect, when when the charge is not fully developed, the battery seems to remember to what extent its capacity was used, and in the future it no longer charges above these parameters;
  • small capacity and a small number of charge and discharge cycles;
  • exposure to self-discharge, when an unused charged battery gradually loses its charge;
  • high toxicity at opening the can due to the cadmium battery included in the battery.

In order for the new battery for the screwdriver to not lose capacity, the first few times it needs to be charged for 10-12 hours, even if the indication appears that it was charged much earlier. In the process of working, it is better to use the battery until it is completely discharged, and then immediately connect it to the charger until it reaches full charge.

Nickel-metal hydride elements in modern screwdrivers are also common. They consist of environmentally friendly elements, but are more expensive than nickel-cadmium batteries. They have lower self-discharge and memory effect and a greater number of charging cycles than NiCd-type cells. But they are afraid of low temperatures and in the discharged state also lose their characteristics.

The most expensive are lithium-ion batteries, which, in comparison with the first two types, have significant advantages:

  • have no memory effect;
  • almost not subject to self-discharge;
  • Designed for more charging cycles and provide higher capacity
  • They are compact in size, since a smaller number of batteries (cans) is required to set the desired battery voltage.
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Each element of a lithium-ion battery has a higher rated voltage, so they are used less than in other types of batteries

Of the disadvantages of batteries of this type should be noted their short service life. Three years later, lithium begins to decompose, the battery loses its capacity without the possibility of recovery.

Typical malfunctions of the screwdriver battery

Despite the fact that the screwdrivers are equipped with different types of batteries, they all have the same design and similar malfunctions. The most common failures of this device are:

  • loss of capacity by one or more batteries;
  • mechanical damage to the battery circuit (tearing off plates connecting banks to each other or to terminals);
  • drying of the electrolyte;
  • decomposition of lithium in elements of the type Li-Ion.

Loss of battery capacity is the most common screwdriver battery defect. Its essence is that the loss of charge capacity of at least one battery does not make it possible to fully charge the remaining banks. Receiving a low-quality charge, the battery is quickly discharged.

Such a malfunction may be a consequence of the memory effect or drying of the electrolyte in the banks due to their heating during charging or under load. This defect in batteries of any type can be eliminated independently without contacting a service center. In this case, you can try to repair the defective elements or replace them. It will not be possible to restore only lithium-ion battery cells that have lost capacity as a result of lithium decomposition. Such banks can only be replaced with new ones removed from a dead battery pack.

A screwdriver battery malfunction can be caused by the loss of the capacity of one or more batteries, so it can be easily fixed by replacing them with new or obviously working

DIY battery repair for a screwdriver

Most defects of the battery pack of the screwdriver can be fixed independently if you know the cause of the malfunction and methods of dealing with it.

Diagnostics of faults in the battery of a screwdriver

Before proceeding with the battery repair, it is necessary to carry out its diagnostics and identify the cause of the malfunction. To do this, you must:

  1. Fully charge the battery pack. Previously, the nickel-cadmium or nickel-metal hydride battery must be discharged to zero to avoid the manifestation of a memory effect.
  2. Disassemble the battery case by removing its cover. It can be screwed or glued, which makes it somewhat difficult to disassemble. In the second case, to remove the lid, you need to use a sharp scalpel or knife to walk along the glue joint, and then, gently prying with a thin screwdriver, disconnect the lid.

The battery cover can be attached to its housing with screws or glue

Visual inspection to determine the presence of mechanical damage, open circuit, as well as swollen or leaked battery cans.

After disassembling the battery pack, the contents are visually inspected for obvious defects.

Video: Replacing Items in a Cordless Screwdriver Battery


Measure the voltage on each of the batteries with a multimeter. For batteries of the NiCd or NiMh type, it should be within 1.2–1.4 V, and for lithium-ion cans, 3.6–3.8 V. On each bank, the measured value is better written in pencil to avoid confusion.

By measuring the voltage on each bank, you can find all the faulty elements

Load the battery by connecting a normal car light or resistance to the output contacts.

By connecting the lamp, we allow the batteries to work to show the voltage drop under load

  • After holding the battery under load, again measure the voltage on each bank and find the batteries on which the maximum drawdown has occurred. These are the defective elements.
  • Video: how to completely discharge a screwdriver battery

    Having found faulty batteries, it is necessary to decide on the method of their repair. Two options are possible here. The first is to reanimate defective batteries by flashing them with a higher voltage current or add them to cans of distilled water if the electrolyte dries. But these measures are temporary, in the future, the malfunction may occur again. effective is another repair method, which consists in replacing defective batteries with new or used ones, but obviously working.

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    Video: Search for defective batteries in a screwdriver battery

    Battery Recovery

    Recovery of the lost battery capacity is possible only for batteries with a memory effect. These are nickel-cadmium and nickel-metal hydride batteries. To do this, you need a more powerful charger with adjustable voltage and current settings. Having set the voltage to about 4 V and the current strength of 200 mA, we apply this current to the batteries in which the maximum voltage drop is detected.

    You can try to repair defective batteries by compression or compaction. This procedure is a dilution of electrolyte, the volume of which in the battery bank has decreased. To do this, you must:

    1. Make a hole as thin as possible in the defective battery, in which electrolyte boils, in the end surface from the minus side of the contact using a thin drill or punch.
    2. Pump air from a can with a syringe up to 1 cm 3.
    3. Using a syringe, inject 0.5-1 cm 3 of distilled water into the battery.

    A small hole is made in the battery case through which air is pumped out and about one “cube” of distilled water is poured

  • Seal the cans of the battery with epoxy.
  • To equalize the potential, discharge all the banks of the battery by attaching a third-party load, which can be a regular 12-volt light bulb, and then fully charge the battery. Repeat charge-discharge cycles 5–6 times.
  • The procedure described in paragraph 5 can, under certain conditions, restore the battery’s performance if the memory effect is the cause of its malfunction.

    Video: screwdriver battery capacity recovery process

    Battery Replacement

    The most effective way to repair the battery of a screwdriver is to replace a defective can. To do this, you can use a new battery, which today can easily be found on sale, or remove a working jar from a dead battery pack. Replacement work must be performed in the following sequence:

      Remove the faulty battery from the battery circuit. Considering that they are all interconnected by plates, mounted on spot welding, it is best to use side cutters for this purpose. In this case, leave the shank of sufficient length on a working jar in order to be able to solder it to a new battery.

    On serviceable banks, shanks must be left so that they can be soldered; on a faulty bank, this is optional

    Solder a new battery in place of the remote defective jar, observing the necessary polarity. The positive output is soldered to the negative output of the “neighbor”, and the negative output, respectively, to the positive. To do this, you need a soldering iron with a power of at least 40 W and soldering acid. If it was not possible to maintain a sufficient plate length, you can connect the cans with a copper conductor.

    A soldering iron with a power of at least 40 W and soldering acid are used for soldering

    Assemble the batteries in the housing according to the same scheme in which they were placed before the repair.

    After installing a working jar, the entire chain needs to be put back into the battery box

  • Perform charge equalization on each bank by repeating several times the charge-discharge cycle. Then check the voltage potentials on each bank with a multimeter. They should be at the same level. 1.3 V.
  • It is important not to overheat the jar when performing soldering work. Therefore, you cannot hold the soldering iron tip on the battery for too long.

    Repair of battery packs with lithium-ion banks is carried out similarly. The only thing that complicates the task during the repair is disconnecting the batteries from the control board. In this case, only one repair method is applicable. the replacement of a defective can.

    Video: how to properly solder the banks of the screwdriver battery

    How to remake a screwdriver battery for lithium-ion batteries

    Often owners of nickel-cadmium batteries screwdrivers want to remake their batteries for lithium-ion batteries. They are attracted by the advantages that can be acquired by such a rework of the battery pack:

    • lighten the weight of the screwdriver, which will require a smaller number of batteries with the same battery capacity and voltage;
    • get rid of the memory effect, which is not found in lithium-ion type batteries;
    • reduce battery charging time.

    In addition, with a certain assembly scheme, the charge capacity can be doubled, which means that the working time of the screwdriver from a single charge. The advantages, of course, are obvious, but this solution has its drawbacks, which you also need to know in order to weigh the pros and cons. Of the negative aspects of adapting the battery of a screwdriver for lithium ion banks, it should be noted:

    • higher cost of lithium-ion batteries;
    • the need to maintain the charge level of the cell strictly in the range from 2.7 to 4.2 V, for which it will be necessary to additionally install a charge-discharge controller board in the battery box;
    • large sizes of Li-Ion batteries, which require ingenuity and imagination to place them in the battery of the screwdriver;
    • the inability to use the tool with such batteries in low temperature conditions.
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    But if the decision to replace the nickel-cadmium batteries is still made, then proceed further in the following sequence:

    1. Decide on the number of lithium-ion batteries and their electrical characteristics. For example, for the most common screwdriver operating on battery with a rated voltage of 14.4 V, it is better to take 4 lithium-ion cells, the total maximum voltage of which will be 4.2×4 = 16.8 V. Here it is necessary to take into account that immediately after starting work on new batteries the voltage on them will sag and will be equal to 14.4-14.8 V. If the capacity of the battery box allows, you can take 8 such cans, forming 4 pairs of them with parallel connected batteries. This will increase the battery capacity by 2 times.
    2. Choose a controller board for 4 batteries. Its parameters should correspond to the discharge current and the rated voltage of the selected batteries. In this case, the working discharge current should be 2 times less than the maximum permissible value of the battery discharge current, which is usually 25–30 A. Therefore, the board must be designed for a current of 12–15 A.

    The controller board must be designed to work with the required number of batteries and is designed for their operating discharge current

    Disassemble the battery box of the screwdriver and remove all nickel-cadmium cans from it. Cut the entire chain with wire cutters or side cutters, leaving only the top element with contacts for connecting to the tool. The thermistor can also be removed, since the controller board will now monitor the battery overheating.

    From the chain of old cans you need to leave only an element with contacts for connecting to a screwdriver

    Assemble a circuit of lithium-ion batteries by soldering them in series, and connect the controller board according to the circuit, observing the polarity.

    When connecting the controller board to the lithium-ion battery circuit, the polarity must be observed.

    Place the assembled structure in the battery box. Lithium-ion batteries are best placed horizontally.

    It is better to place lithium batteries in the battery case of the screwdriver horizontally

  • Close the battery cover by installing a battery with old battery contacts on horizontally stacked batteries.
  • It may turn out that the assembled structure cannot be charged from an old charger. Then you need to install an additional connector for a new charge.

    Video: Replacing Li-Ion Cadmium Batteries

    How to store the batteries of a screwdriver

    For the battery of the screwdriver to last as long as possible, it must be stored correctly, especially when it is not used very often and with long interruptions. In this case, you must follow some rules.

    Cadmium-based battery packs have a memory effect that reduces battery capacity when the charge is not fully developed. Therefore, batteries with NiCd and NiMh batteries should be stored in a discharged state, and devices with lithium-ion batteries should be charged at half the capacity of the cans.. This level can be achieved in a time equal to about 65–70% of the usual full charge.

    If the battery pack of your screwdriver is quickly discharged and does not hold a charge at all, do not rush to throw it away and buy a new one. Its service life can easily be extended using the recommendations above. This will save you from unnecessary costs, because the battery of a screwdriver costs more than half the cost of the entire tool.