Tool Batteries - Storage, Performance, Deep Discharge...

Interesting from the battery world

Tool Batteries - Storage, Performance, Deep Discharge...: deep

The battery - or more accurately, the battery - is an energy storage that can be recharged for a limited time. He is thus different from a battery that has only a limited amount of energy and is unusable when reaching the output quantity. The use of batteries is thus already advantageous from an economic point of view.

The accumulator was invented in 1803 and a lot has happened since then. Even though the most well-known types of rechargeable batteries, the lead-acid accumulator, have existed for more than 150 years, its properties have changed considerably.

For the handyman but the battery was only 1962 interesting, as Black + Decker the first cordless drill presented. It was operated with a nickel-cadmium battery. Today are Lithium-ion battery the standard and deliver a lot of power with a very small design.

Meanwhile, the composition can be adjusted so that batteries are able to deliver consistent performance over a long period of time or achieve tremendous peak performance. Manufacturers are investing tremendously in the development of their batteries to establish themselves in the fast-growing market.

Batteries allow the mobile use of tools and other electrical aids. But battery is not the same battery and, above all, are battery components, they are very sensitive to a wrong charge or incorrect storage. They can quickly lose their performance or even suffer irreparable damage. The right handling is therefore the alpha and omega for a long battery life.

Often it is also difficult to ask which type of battery is the right one. Here are terms such as Memory effect, charge capacity, deep discharge or fast charge, But what do they mean? Added to this is the question of what capacity a battery needs to be used effectively.

We would like to give a deeper insight into the battery world and answer questions that may arise when purchasing the new cordless tool.

Which battery is the right one?

Tool Batteries - Storage, Performance, Deep Discharge...: tool

Bosch IXO - The first tool with a Li-Ion-AkkuNickel-Metallhydrid-Akku (NiMh)

Who has the choice, has the agony and the question between mainly three different battery types - NiCd nickel-cadmium, NiMH nickel-metal hybrid and Li-ion lithium-ion battery. Batteries that have their advantages and disadvantages.

Nickel Cadmium Battery (NiCd)

NiCd cells deliver one Voltage of 1.2V, which however decreases with the load. Due to the very low internal resistance, they are capable of enormous peak loads, even in the most extreme temperatures. NiCd batteries are therefore extremely robust and suitable for the toughest tools, Due to the However, toxic cadmium has already been banned from use in many sectors, and as of December 31, 2016, even battery-powered tools have been dropped underneath. Replacement batteries for older tools, however, will certainly be available as replacement parts. Nevertheless, one should certainly no longer rely on cordless tools with NiCd batteries. The disadvantage here is especially the self-discharge, so longer unused batteries in case of need like to be empty.

NiMh batteries deliver, like NiCd batteries one Voltage of 1.2V per cell. They replace the now no longer freely available NiCd batteries. Its almost twice the energy density improves performance and also protects the environment without toxic cadmium. However, NiMH batteries are not quite as robust and unsuitable for use in colder temperatures, Their sensitivity to deep discharge or polarity reversal also requires an intelligent charger that monitors the charging current and optimally charges NiMh batteries. NiMh batteries therefore find only limited use with new cordless tools and replace mainly previously used NiCd batteries.

Lithium ion batteries (Li-Ion)

With the IXO, the best-selling power tool, the first tool received a Li-Ion battery in 2003 and was quite messy with the world of cordless screwdrivers and other mobile devices. You own a lot high energy density, no memory effect, increased life, only minimal self-discharge and can be partially unloaded and reloaded without hesitation. Thus, they improve the durable and performance-hungry work in the commercial environment as well as the opportunity for many private users. Li-ion batteries are therefore now the basis of almost all cordless tools.

Important terms for battery technology explained

Tool Batteries - Storage, Performance, Deep Discharge...: storage

Integrated battery status display against total discharge

In order to be able to make the right choice of battery, it is important to know the data and some technical terms, which we would like to briefly explain here:


Under stress, each battery understandably loses its charge. Depending on the type of battery, however, it does so to a certain extent as well when not in use. The lost energy can not be used and lead to an empty battery when stored for a long time. While NiCd batteries still had to live with a monthly self-discharge of up to 15%, Li-ion batteries lose just 3% of their power depending on the storage temperature. Casual users should therefore always pay attention to low self-discharge. Anyone who uses his cordless tool on a daily basis is only slightly influenced by self-discharge.

deep discharge

A deep discharge is spoken, when the power of the battery drops so low that no power can be removed, The discharge end voltage is reached. While NiCd batteries are not affected in their function and should be emptied to prevent the memory effect even now and then completely, NiMh batteries may only briefly subject to deep discharge and Li-ion batteries are thereby even destroyed. Here it is even dangerous and Deep-discharged Li-ion batteries should no longer be used, In the battery copper bridges form, which lead to a short circuit, enormous heat and possibly fire or even explosions. Own modern cordless tools for safety, a deep discharge protectionwhich is installed in the battery or the tool. The deep discharge is therefore prevented.

Quick charge

Older NiCd batteries were used to charging 12 hours and more. These times are long gone and Li-ion batteries charge in simple chargers in 3 to 5 hours, With so-called quick chargers, which offer significantly more charging current, can be Charging process but even reduce to one hour - the fast charge, Even if the technology allows it, the fast charge is only partially advantageous. The fast charging process requires a lot from the battery, which can significantly shorten life expectancy. Fast charging should therefore only be done with sophisticated technology that monitors the charging process and the temperature of the battery.

Trickle charging

Tool Batteries - Storage, Performance, Deep Discharge...: tool

Modern chargers control the charging process

When a battery is charged, it has reached its charging capacity and must not be charged further. The charging current must therefore be interrupted. The trickle charge continues to emit (usually in pulses) a small charging current, which counteracts the self-discharget. The full charge is thus obtained.

discharge curve

Depending on their design and composition, rechargeable batteries have a different discharge curve. This indicates how the battery loses its voltage in relation to the consumption, For example, Li-Ion and NiMh batteries have a very straight-line discharge curve. After a short drop, the voltage decreases only slowly, until it suddenly drops and the battery is empty. Even an almost empty battery therefore still offers a similar performance as a full battery. The discharge curve of NiCd batteries, however, drops steadily, so that the voltage drops steadily with the discharge.

Memory effect

In principle, each battery has a memory effect, which occurs but different levels and is repairable or durable. Especially NiCd batteries were very susceptible to this. If they were only half unloaded and recharged several times, the battery "noticed" this discharge - hence memory - and could subsequently only be used over this area, Sometimes a repeated change of full charge and discharge lifted the memory effect, the process was unsuccessful, the battery was defective. Today, the composition of the batteries has been adjusted so that hardly any memory effect is recorded. A complete discharge of the battery before reloading is therefore not necessary, but is recommended now and then after several charges.


Tool Batteries - Storage, Performance, Deep Discharge...: tool

Further development allows more capacity with the same size

The voltage of the battery and thus of the tool is given in volts and can be between 3.6 and 36 volts (or more) for cordless tools. The tension, however, only partially says something about the performance of the tool. Although higher voltages are usually also associated with more powerful machines, by means of different gear ratios, even a tool with a lower voltage can achieve a higher performance than a tool with a larger voltage.


Each battery has a certain ability to store and release energy. This value can be very different and depends not only on the size. The Battery capacity is in ampere hours (Ah) and how many hours a device can run at the specified amperage. If the tool has a power rating of one ampere, a 2 Ah battery can power it for 2 hours. 4 Ah would double the duration as well as half the power consumption of the tool.

What performance does a tool battery really need?

Tool Batteries - Storage, Performance, Deep Discharge...: performance

18 V batteries with 1.5 Ah and 2.5 Ah

This question can not be answered flatly and depends mainly on the tool and the work performed. In addition, of course, the possibility of a removable battery.

Take as an example the popular Cordless Drill:

Assuming an average wrench with a power consumption of 150 watts and a voltage of 12 V, this results in a power consumption of 12.5 A. If the associated battery delivers 2 Ah (1 A in 2 hours or 2 A in 1 hour), the cordless screwdriver can Last 9.6 minutes to be operated. What does not sound like much at first, however, can be very long in use. A small screw is screwed in less than 3 seconds, which at 9.6 minutes already corresponds to almost 200 screws, which certainly do not use the screwdriver to 100%, which increases the number even more.

18 V batteries with 1.5 Ah and 2.5 Ah

Anyone who has been working with a cordless screwdriver for some time knows that a 2 Ah battery is absolutely sufficient under normal conditions. But the bigger the voltage, the bigger the battery should be. For small screw jobs with one 10.8 V screwdriver can be a 1.5 Ah battery already be sufficient. At a 18 V screwdrivers should have at least 2 Ah or more.

Another important criterion is the availability of a replaceable battery. Fast Chargers charge a battery today within an hour on average. Under normal conditions, a cordless screwdriver with a 1.5 Ah battery is even in intensive use over an hour in use, because rarely is permanently screwed. The removable battery is already charged during this time and can be replaced with the used battery.

The question arises whether to use a battery with 4 Ah or rather two batteries with 2 Ah each. Is the Variant with replaceable battery preferable. Only it allows a permanent use. A larger battery lasts longer, but if it is empty, it must be charged in a forced break. Here a change battery is clearly in the advantage.

Proper storage of batteries

Batteries have a self-discharge that depends on the ambient temperature as well as the state of charge. Added to this is the fact that batteries react differently to a deep discharge and even here permanent damage or explode, It is therefore important to know its batteries and tools. The following overview indicates, below which conditions optimally stored batteries should be. The information can of course vary from manufacturer to manufacturer and serve only as a guide

self-dischargeoptimal charge statestorage temperatureDistance of recharges
NiCd batteryabout 15% a month40% (non-critical)20° C3 months (uncritical)
NiMH batteryabout 20% a month40%20° C3 months
Li-Ion Batteryabout 2% a month50 - 75%18 - 25° C1/2 year

Special features of lithium-ion batteries

Lithium-ion batteries are undoubtedly one of the biggest achievements of the battery technology. They achieve unprecedented performance, as well as storage capacities with special quality features, but are also somewhat more complicated to use.

Tool Batteries - Storage, Performance, Deep Discharge...: deep

Electronics prevents deep discharge

If you hear older do-it-yourselfers talking about cordless tools, it is often said, "Too heavy and no performance." or "If you need them, they are all anyway." With the introduction of lithium-ion technology, such statements are a thing of the past, even if some people find it difficult to convince them. Li-ion batteries are smaller, more powerful and expand the field of application considerably.

Of course, all batteries - even Li-ion batteries - a self-discharge. However, Li-ion technology can reduce these to a minimum so that they are almost negligible. With a loss of 1-3% per month, a 100% charged Li-Ion battery is theoretically discharged completely autonomously only after years. However, it is not that easy, because the self-discharge depends on the ambient temperature. Li-ion batteries like it a bit cooler, but are used in very cold conditions only limited. Even below 10° C, the performance can be severely limited, Similarly, too high temperatures above 60° C can destroy the structure of the battery. The optimum working, loading and storage temperature is between 18 and 25° C. In the living room lithium-ion batteries are therefore in good hands.

Lithium-ion batteries offer the advantage of being them loaded very fast can be. Depending on the performance of the charger, an 18 V battery with 2 Ah already has its full capacity after one hour. As with all operations, however, fast is not always good. Too fast charging causes the battery to age faster. The influence is certainly not immediately noticeable, but shortens the life of the battery.

A particular advantage of Li-ion batteries is their minimal charging behavior in addition to minimal self-discharge. Unlike older NiCd batteries, they have no memory effect. They can be reloaded at any time, which does not affect their capacity. Many small loads affect life expectancy. If a battery with 2000 charge cycles is specified, this means the complete discharge and recharging. However, if the battery is already charged from a power level of 50% to 100%, this corresponds to only half a charge cycle. Considering the fact that the While complete discharge is detrimental and Li-ion batteries tend to age under full charge, many smaller charges are even beneficial to the battery life, The optimal Storage should therefore be at a battery level of 55 - 75% lie. The charge reduces the aging process and offers scope for deep discharge.

The above points show that lithium-ion batteries combine many advantages, but also one careful handling and special control, They must never be deeply discharged and require a controlled charging process. Therefore, use only electronically controlled chargers and replace defective batteries only with original batteries of the same manufacturer. There is no guarantee that the complex interaction between battery, monitoring electronics and tools will work 100%.

Why are there Li-Ion batteries with 10.8 and 12V or 18 and 20V

While NiCd batteries or cells have a nominal voltage of 1.2 V and thus result in combinations of several cell batteries to 6, 12 or 18 V, the specification for lithium-ion batteries is not clearly defined. Li-ion batteries have an initial voltage of about 4 V, which, however, reduces to 3.6 V after a short load and leveling. Now, if three such cells are connected, the two voltage specifications (3 x 4 and 3 x 3.6) of 12 V and 10.8 V. The voltage specified or advertised is not mandatory. In Germany, the smaller one is mainly indicated, whereby many manufacturers here now switch to the American model of the larger initial tension. They usually produce for several countries and thus minimize the effort of the different labels. So if identical tools are found with Li-Ion batteries advertised with 10.8 V and 12 V or 18 V and 20 V, these are the same batteries that were only planned for different markets.

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