Storing and charging batteries correctly

How to optimize battery life!

Batteries accompany us every day. Whether for mobile phones, laptops, e‐bikes or batteries for tools. Nevertheless, there are some things we can do better in daily use to optimize their service life. In this battery guide, you will learn how to properly charge and store batteries to prevent a loss of capacity, or at least how to slow it down. We will clarify the myth of the memory effect and refresh your knowledge of the most important points in handling batteries. What was that about watts, volts and ampere‐hours? Here comes your portion of battery knowledge.

Why do batteries lose capacity? How does a battery age?

In this context, “aging” means the loss of capacity. A prime example of batteries losing their capacity with time is what happens with smartphones.  After several years of use, they run out of juice faster and faster. This is due to the chemical processes that take place in the battery during charging and discharging. The Lithium‐Ions self-discharge and this inevitably leads to a loss of capacity in the battery at some point. With that being said, a battery may age even when not in use, for example, when left in direct sunlight and overheating. Therefore, aging is quite normal with a battery, but there are still certain things you can do to slow down the loss of capacity and give you a longer battery life.

Charging the batteries correctly: That is how it works!

Plug in the charger and that’s it? Unfortunately no, because there is also potential for optimization when recharging. The charge current, measured in amperage (A), for example, is a deciding factor, because it makes a big difference whether batteries are charged quickly or slowly. The higher the charging current, the shorter the battery life. You can see with which charging current your charger is using by the amperage on the data label: chargers with 3A are more than sufficient to charge your tool battery in most cases.

Continue with the right time for charging.

When are you supposed to charge? What is the memory effect?

But what about the memory effect? Does it still exist or is it a myth? Nowadays, thanks to Lithium-Ion batteries, we can fortunately say that the effect no longer exists. But what is the memory effect? The memory effect occurs when batteries are temporarily charged when they are not yet empty. Especially with the now obsolete nickel‐cadmium batteries, this led to the fact that they “memorized” the charge level and then could no longer be charged to full capacity during the next charging process. Nowadays the devices are equipped with Lithium‐Ion batteries. These not only have a significantly longer running time, but the memory effect is also no longer important. Nevertheless, even with the new energy sources, it is decisive how long and when they are charged:

Basically, it should be noted that the capacity of the batteries deteriorates if the battery is connected to the charger for too long. It is the last percent of the charge in particular that places a particular strain on the energy storage system. On the other hand, a Lithium‐Ion battery should not be completely discharged. The memory effect is no longer important, but as mentioned above, modern Lithium‐Ion batteries can become deeply discharged.

What is a deep discharge?

Modern rechargeable batteries switch off automatically when the charge falls below a certain minimum level. A deep discharge happens when the capacity has been worn out. This usually happens when batteries are stored empty and then discharge themselves even further. If self‐discharge takes place for too long, deep discharge occurs, which can cause permanent damage. You might ask yourself, can such deeply discharged batteries still be saved? Yes, sometimes.

Our Power X‐Change chargers are equipped with a refresh mode. If a battery is plugged into the charger whose deep discharge is not yet too far advanced, the battery can still be “saved” in many cases. The charger charges the battery very carefully until the minimum charge level is reached again. It can then be charged again as normal.

Interchanging: Can I do that?

A Lithium‐Ion battery feels “most comfortable” at a charge level of 30 to 60 percent. By the way, this corresponds to exactly two illuminated LED on the charge status display of Power X‐Change batteries. Exactly contrary to the older batteries, a short break in between is very useful in case of Lithium‐Ion batteries.

A small example: The Einhell 4–6 Multi‐Ah battery can be used both as a 4.0 Ah battery and as a 6.0 Ah battery. As a 4.0 Ah battery, the cells are not fully charged or discharged. It always moves within this optimum range. This means that if the battery is set to 4.0 Ah, the cells are protected and the battery life can be increased by more than 300 %.

Once the charging is complete, the next step is to store the battery correctly.

Store Lithium-Ion batteries correctly: Where, how and for how long?

The room for storage should be dry and protected from dust. A temperature between 10–40 °C is recommended for batteries, but a cool room temperature of 15–20 °C is optimal. Since higher temperatures accelerate aging, batteries should also be protected from sunlight and direct heat. A too low temperature, for example below 0 °C, should also be avoided. In winter, therefore, the batteries of cordless gardening tools should not be stored in the garage, but rather in a frost‐free cellar or directly in the house.

During storage, care must also be taken not to store the battery for too long. Ideally, a period of up to six months should be observed. During long storage, the battery should have a state of charge of approx. 30–60 %. With Power X‐Change batteries, you can recognize this by the fact that 2 LED are still lit. In addition, the battery should be stored separately from the charger to prevent premature aging.

Key figures for lithium-ion batteries

Various factors play a role with batteries: The weight, for example, affects how user-friendly a device is. Half a kilo may not make any difference with a cordless lawnmower, but 500 g can make a big difference when working with a cordless drill for a long time. However, the most important battery figures are probably ampere-hours (Ah) for running time and watts (W) for power.

The whole thing can be compared very well with a car. While the ampere-hours in a car stand for tank capacity or range, the wattage is responsible for the power, i.e. the horsepower in a car.

This applies to the comparison within a power class, which is specified in volts (V). The 18V and 36V voltage classes have established themselves in the market for tool batteries. Who can still remember the physics lessons at school, knows 1 W = 1 V x 1 A. For example, our 4-6 Multi-Ah battery has 18V x 75 A = 1350 W maximum power, but this also means that if the voltage (Volt) doubles, the power (Watt) doubles as well.

Did you know? Instead of using your own 36V batteries, the Einhell Twin-Pack technology allows you to easily combine two 18V batteries into one 36V device for the most powerful devices on the Einhell 18V battery platform, Power X-Change. This saves money and protects the environment, with double the power.

Myth: Why 18V and 20V is actually the same

18V = 20V? No, we have not made a mathematical error here. In the case of tools, it currently occurs more frequently that the 18V devices are presented as 20V devices. Is that a lie, then? Yes.

Lithium‐Ion batteries consist of battery cells with a nominal voltage of 3.6V. However, the maximum voltage can be up to 4.0V. If now several accumulator cells are connected in series, the result is, 5 x 3.6V = 18V and 5 x 4.0V = 20V. However, the technology used is the same. Don’t let yourself be fooled!


In summary, modern rechargeable batteries require careful treatment, even if they are not as sensitive as older energy storage devices. Nevertheless, with our tips, you can easily extend the life of your batteries and enjoy their cordless energy even longer.