Batteries for screwdrivers – service and repair

With all the advantages of cordless tools, there is one significant drawback – any battery has its own service life. No matter how hard we try, sooner or later we are faced with the question of either replacing the screwdriver’s batteries, or buying a new one (screwdriver or battery). Or maybe we’ll try to deal with the battery itself, maybe not everything is as complicated as it seems at first glance?

In this article we will talk about the most common types of batteries for screwdrivers and try to describe several options for restoring a battery, talk about the device of a battery for a screwdriver.

Battery types for screwdrivers

There are a lot of technologies for manufacturing batteries for screwdrivers, but we will focus on the most common ones. Lead-acid batteries were one of the first to appear and began to be widely used. The main area of ​​their use to this day is the automotive industry. Simplicity in manufacture and maintenance makes these batteries the most demanded. However, their dimensions leave much to be desired, it is extremely inconvenient to use such batteries for powering power tools – low power, the significant weight of the power supply makes such a tool ineffective. The situation is quite different with more modern nickel-cadmium batteries. Since their invention to the present day, these rechargeable batteries have been one of the most common power sources for cordless tools..

Low cost, significant battery capacity with small dimensions and weight makes the nickel-cadmium cell very popular among tool manufacturers. The electromotive force (electromotive force) of a nickel-cadmium battery is 1.37 V, and its specific energy is 45 to 65 Wh / kg. Depending on the design of the battery, its mode of operation (long or short discharges, correct battery charge) and the purity of the materials used, the battery life is from 1000 to 3500 full charge-discharge cycles.

However, there are also disadvantages – the production of nickel-cadmium is extremely toxic. Currently, the European Union has banned the production of this class of batteries on its territory. Nickel-metal hydride batteries are the newer generation of tool batteries and are the second most commonly used. Nickel-metal hydride compounds, robust enough for use in tool batteries, were developed in 1980.

One of the advantages of nickel-metal hydride batteries is a fairly high environmental safety of the production and disposal of cells, an almost complete absence of the memory effect, however, the high self-discharge current of the battery somewhat spoils the opinion about these batteries. You need to store such batteries charged, with a long idle time (more than 1 month), it is advisable to completely recharge the battery.

Lithium-ion batteries are a promising trend in the development of all cordless tools. Lack of memory effect, lighter weight and dimensions, high capacity, fast charge – these are the main advantages over traditional batteries. However, the high production cost makes these batteries less desirable. Not every consumer is ready to shell out a tidy sum for a tool with, albeit progressive, but very expensive batteries. Lithium polymer batteries are only new to the market and are hardly used in traditional cordless tools..

We have provided general characteristics of the most common rechargeable batteries. Given the fact that nickel-cadmium batteries are most often encountered, we will try to “revive” this type of batteries after a long service life..

We repair the battery for a screwdriver

As a test case, we use the Bosch GSR 12-2 professional cordless screwdriver, which is equipped with nickel-cadmium batteries. For example, look at a MAKITA battery (it is red) and a Chinese product (labeled 12V and 18V). As in the case of repairing a screwdriver gearbox, a traditional service can only offer the replacement of a complete spare part. But not everyone decides to buy, knowing the cost of a new battery. Let’s try to solve our “energy problem” in practice.

Unlike the BOSCH battery, the MAKITA battery is not so easy to disassemble – it is completely sealed and made “disposable”. We coped with the Chinese-made battery with ease – three self-tapping screws allowed us to look inside the block. You can talk for a long time, but it is better to see and understand once how a “branded” instrument differs from what is sold to us “at an affordable price”. Thin power wires, poor-quality soldering of connecting buses, lack of a temperature sensor, lack of a charge equalization device in the banks of the battery pack, batteries are fastened together with tape … The list goes on for a long time. But it’s better to see once.

The battery of the Bosch GSR 12-2 professional screwdriver has a collapsible design. The Bosch company is generally famous for the fact that not only does it completely recycle and dispose of its products, but also actively uses recovery technologies, for example, the restoration of car generators and starters. The battery was actively used for 3 years in the conditions of the construction site, and during this time it was not only slightly rubbed, but “thanks” to the carelessness of the builders, it stopped holding the capacity. The memory effect played a role. Compare the “insides” of batteries from different manufacturers, the differences are visible at a glance.

In order to remove the elements from the battery case, we have to remove the factory plastic seal on one of the four screws and slightly press the locking mechanisms that secure the battery to the screwdriver, remove the top cover. As we can see in the photos, all rechargeable batteries consist of a certain number of small batteries. Banks of these batteries can have different sizes and, accordingly, capacity. The battery pack is assembled from separate batteries of the same size and capacity. The screwdriver battery has four contacts: two power contacts (plus and minus as on a regular battery), a special control contact that connects the temperature sensor inside the battery to the charger (in photo # 4, two thin wires from the temperature sensor and a thick power wire are clearly visible). This is a very important option. This thermal sensor monitors the temperature of the battery cells during charging. If the design temperature is exceeded, the sensor breaks the electrical circuit and thereby prevents the destruction of the elements.

The so-called “watch” charger (the battery is charged within 1 hour) uses high currents, which, in the absence of a temperature sensor, can destroy the battery. Another important function is implemented in rechargeable batteries of famous world manufacturers – a device that allows you to uniformly discharge and charge all battery cells. As we saw with you earlier, cheap Chinese rechargeable batteries are completely devoid of these “protective and preserving” options. And this is despite the fact that many products are equipped with devices for fast battery charging. We have described above what such a reduction in the design cost can lead to. Not all batteries have a service contact. In this case, in the Bosch battery, this contact is connected to a special resistance and serves to equalize the charge in all battery banks (in photo # 6, this resistance is clearly visible in the area of ​​the battery contacts).

The battery was in such a condition that it would not be possible to perform any work. Its capacity was barely enough to tighten a dozen standard screws, and this after it was fully charged. The reason for this behavior of the battery may be a failed bank that makes up the battery of the screwdriver. All cans in a battery are connected in series with each other (like batteries in a flashlight). The high internal resistance of a failed battery bank prevents the remaining battery cells from being charged. As a result, the battery cannot be fully charged. It is best to search for faulty cells after the battery is fully charged. We have to not only measure the voltage of the battery as a whole (using a standard voltmeter), we need to find the very faulty elements, which we will then change. It should be remembered that taking measurements on each battery cell separately, the result should be in the range of 1.2 – 1.4 V. If the cell voltage is less than 1.2 V, then this indicates a malfunction of this cell.

Most likely, it is such a bank that will interfere with the normal operation of the entire battery. After we have identified the faulty element, we have to check the battery and make sure that our actions are correct. To do this, we assemble the battery and begin testing it under load, simulating a normal workflow. To do this, you can, for example, tighten screws, self-tapping screws, in a word, do all the work that you usually do with this tool. After a short period of time, the battery quickly loses its capacity. We have to re-disassemble the battery and make sure that our “find” is correct. The measurement result showed that this particular element after the “load” has the lowest residual voltage. Now we have to either try to restore this element in the battery for a screwdriver, or completely replace it with a workable (or new) one.

Let’s consider the option of “reanimating” the old battery. Constant high loads during the operation of the tool often lead to the fact that individual containers (cans) of the battery lose their tightness and simply dry out, the electrolyte present there intensively evaporates during operation and the cell becomes unusable. It is not for nothing that we called the attempt to restore the working capacity of the battery bank as resuscitation. A short-term exposure to a battery bank with a stronger current can “revive” a damaged cell, partially or completely restoring the processes that take place inside the battery.

Another option for restoring the battery’s performance is gentle compression, deformation of the case. Remember what you did with a discharged battery – you squeezed its case a little with light blows and the battery continued to work for some time. Nickel-cadmium screwdriver batteries are very durable. They perfectly hold a charge, discharging by only 7-10% on the first day after a full charge and then practically do not lose their charge for a long time. However, overheating caused by inrush currents and memory effect can take such batteries out of service ahead of time. If it was not possible to restore the performance of the battery by mechanical action, then it must be replaced.

As always, there are several replacement options. If we are talking about any construction team that works with these cordless tools, then, most likely, there will be old batteries from previously purchased tools. Such is the mentality of our people – to keep “in reserve” even spoiled things. The batteries are quite tenacious and the age of 5-7 years is not so great for them, although at the same time they lose a certain part of their capacity. It is extremely important to use high-quality materials for soldering the elements (corrosion resistance, minimum circuit resistance is the key to high quality of the remanufactured battery). Naturally, it is necessary to act quickly and carefully – high temperatures during soldering can destroy the battery.

The battery is now assembled, but not yet ready for use. Do not forget. That before replacing the cell, we charged and tested the battery, besides, the charge of the replaced cells may differ significantly from the charge of the remaining battery cells. We are going to have the so-called “training” of the battery. This is what will allow to equalize the charge in all banks of the battery. First of all we need a charger. Which does not turn off after a certain period of time. After an intensive charge (about 8-10 hours), it is necessary to allow the battery to cool down to ambient temperature. Just do not speed up this process, let the battery cool down on its own. Before starting work, you need to check the voltage – it should be 1.5-2.5 V higher than that indicated on the battery. The battery must be discharged as much as possible, but do not forget that during operation the battery heats up and it is very important to prevent it from overheating, and the screwdriver itself does not really like high temperatures. For this reason, carefully monitor the temperature of the entire instrument..

After checking the battery, we have to eliminate the memory effect of the restored battery for the screwdriver. To do this, you will have to charge and fully charge the battery several times. To do this, it is not at all necessary to work with a screwdriver, an ordinary light bulb will come to your aid, which will allow you to discharge the battery effectively enough.

Some readers have a natural question – isn’t it easier to buy a new battery? Naturally easier, but does it make sense to do it? The cost of a new battery for the same Bosch GSR 12-2 professional screwdriver is comparable to the price of a new tool (do not forget that a new tool comes with 2 batteries). So isn’t it worth spending some time and extending the battery life for a few more years?

We hope that these tips have not only expanded your knowledge of cordless tools. But in practice, they will make it possible to use the tool more rationally and save money..