How to Find a Faulty Battery in a Screwdriver

How to Find a Faulty Battery in a Screwdriver

A dead battery for a screwdriver can be charged. But if the discharge occurs more often, and the power decreases, these are signs of a battery malfunction. Usually, the owners immediately try to change the damaged block to a new one. But by comparing how much a single battery for a Bosch screwdriver costs with the price of a new tool with two batteries, they often choose a new kit.

Battery Composition and Parameters

The situation is not as sad as it seems at first glance. Sometimes it is possible to repair the battery of a screwdriver with your own hands without financial costs or with small expenses. To know how to repair the battery pack at home, you should get a voltmeter, soldering kit, screwdriver, penknife, get familiar with the types and properties of the elements used in the battery.

The principles of operation of energy-accumulating elements are the same for capacitors and for batteries. A thin layer of dielectric, electrolyte in the case of batteries, separates the two layers of metal foil, which accumulate bipolar charges. When consumers of electricity are connected between the contacts of the layers, the flow of charges moves through it to the opposite layer, doing the job. Thus, the main characteristic of a battery is the amount of accumulated charge, expressed in ampere hours. The common abbreviation A / h or A / h is applied to any battery.

A charge between the plates generates a static electrical voltage. If a charge is allowed to significantly exceed the rated voltage for which the battery is designed, the electrolyte layer will be broken, which will completely destroy this cell. A lower voltage of the charger will reduce the power stored in it. The second parameter of the battery is voltage. One element, depending on the type, keeps the voltage in the range from tenths to several units of volts.

Characteristics of their types

The difference in the chemical composition of the plates and the electrolyte, dimensions, and the relative positions of the components determine for the batteries not only performance, but also cost. As always: the better the more expensive. For screwdrivers, the optimal price-performance ratio is inherent in three types of metal plates. Two are based on nickel with the addition of cadmium (Ni-Cd) or metal hydride (Ni-Mh), one type uses lithium and is designated Li-Ion (lithium-ion battery). Each type has its own characteristics and characteristic malfunctions.

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Nickel-cadmium type is low in price, frost tolerance, long discharged storage. Low voltage on each bank of 1.2 V increases their number in the battery. Negative characteristics include a small number of discharge-charge cycles, high self-discharge, low charge memory, environmentally harmful production and composition.

Nickel-metal hydride batteries are more expensive, but they have lower self-discharge, can withstand more charge-discharge cycles, low-charge memory is not so strong, environmentally friendly production. The charge of the can is 1.25 V. In terms of frost resistance it is softer than cadmium and the shelf life is shorter.

Lithium-ion devices are priced above nickel-metal hydride. They have a high voltage of 3.6 V. The technology pluses. there is no self-discharge and low-charge memory, the capacity is higher than that of other types, the largest number of charging cycles. Cons. the shortest shelf life, the elements are environmentally harmful when disposed of.

Screwdriver Battery Design

Video: How to Find a Faulty Battery in a Screwdriver

The plastic case hermetically seals the contents of the battery with the exception of sockets, metal terminals or contact pins designed for operating charge-discharge currents and, if there are more than two contacts, for charge control.

Since the battery does not work, to repair the battery of a screwdriver, disassembly with opening the plastic case is necessary. If there are screws, they must be unscrewed. In the sealed case, you should deeply scratch the gluing line with a knife and cut or gently drill a shallow hole in it. Then, screwing the conical screw, it is necessary to achieve the appearance of a gap and, helping with a knife or a screwdriver, expand it to the full perimeter of gluing. When assembling after repair, epoxy will seal the gap no worse than before.

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The screwdriver battery device is visible when opening the case:

  • several series-connected batteries;
  • a temperature sensor fixed to one of the elements with a charge current interrupter when the battery is heated;
  • control board, but only in lithium batteries.

However, it is worth starting the diagnosis before opening the case.


For diagnosis, you need a tester or a DC voltmeter, a charger and a little time. It is better to start the search by measuring the battery voltage of the batteries before and after fully charging. The voltage value of the charged elements must be compared with that indicated on the case and measured before charging. The options for the results of voltage measurements will tell How to fix a screwdriver battery:

  1. It was and remains equal to zero.
  2. Equal or greater than nominal.
  3. Remained at the same level as before charging.
  4. Quick reduction of voltage without load and stabilization below the nominal indicated on the housing.

Now the defective item for repair is purposefully determined.

Battery repair for screwdrivers

A screwdriver battery can be restored by a design feature. a serial connection of identical elements. Such a circuit does not allow the simultaneous failure of all battery cans. So, you need to find one or more faulty elements.

  1. The lack of voltage on the contacts of the block is extremely rare. The serial circuit of the connection of the elements will show 0 voltage only when the circuit is broken, and this is determined and repaired. In the disassembled unit, one probe of the voltmeter is connected to the extreme contact of the first in the circuit of the can, and the second is measured in series with the voltage at each contact of the other cans. Contact break in the place of power failure is eliminated by soldering. Solder the contact with the bank quickly, without overheating the battery. Theoretically, a malfunction of the temperature sensor and the interrupter is possible, but in practice this does not occur. If such a rarity has occurred, replace parts that are popular among electrical products. Temporarily short-circuit the breaker contacts before replacing.
  2. In a charged battery, the voltage is normal, and the battery runs down quickly. This is typical only for lithium batteries. Their capacity decreases due to the decay of lithium. Here one element does not help the case, the replacement of all battery cans is inevitable. When buying lithium batteries, you should carefully look at the date of manufacture.
  3. After charging the battery, the voltage is slightly higher than that of a discharged one. The fault is typical for nickel batteries. This is how “memory” manifests itself if the battery was in a semi-discharged state for a long time before operation. Recovery of ni cd screwdriver batteries occurs with a 4-fold cycle of full discharge. full charge. If the procedure did not help, it is worth trying to find and replace the worst banks, as in the following case.
  4. The last variant of the malfunction is manifested by a sharp decrease in voltage immediately after charging, which indicates the presence of a faulty battery. Which one requires replacement is evident from a significantly lower voltage than the others. Batteries similar in manufacturing technology, capacity, and dimensions can be purchased much cheaper than the entire battery.
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Old batteries lose their capacity from drying out the electrolyte. In a critical situation, when it is impossible to replace the can, the hope of a temporary restoration will be given by heating the can to 60–70 degrees or light compression of the case with pliers.

A battery with a restored or replaced battery will not be superfluous, and from two identical faulty batteries, due to the interchangeability of the elements, one working battery can be assembled and you can wait until the purchase of a new tool.