General recommendations

By “storage” in this article we mean periods from a month to six months. This occasional use is what is most characteristic of cordless power tools and garden equipment, that are used in the garage, home workshop, country house or garden plot.

For all batteries, regardless of type, brand and model, there are general rules.

  • During long-term storage, the battery should be disconnected from the power tool or removed from the battery compartment.
  • Carefully wipe the battery and metal contacts with a clean cloth (preferably made of microfiber or other absorbent material) and make sure they are completely dry.
  • It is best to store the battery in a dry (relative humidity no higher than 60%), dark and cool place. Places where there are temperatures below 0 °C and above 50 °C, as well as places where the battery may be exposed to direct sunlight, are absolutely not suitable for storing.
  • Long-term “wintering” of batteries for tools and garden equipment is best tolerated when stored in plastic cases or tightly closed store boxes, which provide protection from dust and moisture, insects and rodents. Batteries can also be stored in airtight plastic containers, such as regular kitchen containers.
  • It is better to choose a shelf made of a material with low thermal conductivity (i.e. wood or plastic, but not metal) as a place for storing batteries. Due to the ability of metal to heat up and cool down quickly, the temperature conditions and microclimate on a metal shelf in an unheated room will be less stable (higher probability of condensation from air moisture even in a closed box or inside the battery).
If stored properly, the battery will last a long time.

Specifics of Li-Ion batteries

Modern cordless tools and garden equipment are most often equipped with lithium-ion batteries. They have a high specific capacity, charge quickly, have low self-discharge, produce stable voltages up to almost full discharge. That's why Li-Ion batteries are perfect for professional devices that requires continuous and long-lasting use, as well as for home models. However, they also have disadvantages: at temperatures below 0 °C, they discharge quickly and can also lose capacity if discharged too deeply.

During operation, fully discharging a lithium-ion battery is nearly impossible due to built-in electronic circuit that shuts off power when a deep discharge is detected, preventing irreversible damage. However, during off-season storage, the battery's self-discharge rate can lead to significant depletion. To mitigate this, it's advisable to partially charge the battery before long-term winter storage, ensuring it's maintained at around 50% capacity. Regularly checking the charge status during storage, ideally monthly, is also recommended to prevent excessive discharge.

Reasons why Li-Ion batteries should not be stored in the cold

Unused power tools are often sent to the far corner of the shed or garage for the winter, left on the balcony or taken to the attic. With proper preservation and preparation for the off-season, the cold will not be too bad for your tool.

Li-Ion batteries react differently to freezing temperatures and require careful handling. Below 0°C, self-discharge processes accelerate notably, as evidenced by common experiences with smartphones on cold winter days. Long-term storage in extreme cold, especially when deeply discharged, can lead to significant capacity loss or even irreversible damage. Thus, storing lithium-ion batteries in unheated environments such as all-metal garages or leaky sheds during winter is not recommended. If leaving tools like a a screwdriver or lawn mower at a cottage for winter, it's advisable to bring the battery indoors for storage in more suitable conditions.

Batteries should not be stored in frost or high humidity.

Note that there is a difference between long-term storage and direct use. It is not uncommon for battery-powered tools to be used in winter. Operation at temperatures below 0 °C is permissible because the battery heats up during operation, which compensates for environmental influences. However, you should keep the spare battery (if you have several) close to your body (e.g. in a jacket pocket) and not leave it out in the cold.

Reasons why Li-Ion batteries should not be heated up

High temperatures pose not only harm but also significant danger to lithium-ion batteries. Exposing them to temperatures above +60°C can lead to spontaneous ignition, while temperatures reaching +130°C can result in explosion. Thus, it's crucial to store battery packs away from sources of heat, including radiators, heating devices, and open flames. Additionally, avoid placing batteries on windowsills, behind glass, or in direct sunlight to prevent overheating.

Ideal conditions for storing Li-Ion batteries

The table below shows examples of recommendations from several different power tool and garden equipment manufacturers that limit the lower and upper limits of the optimal air temperature for storing batteries. All data is taken from the operating manual.

Metabo DeWALT Ryobi Einhell AL-KO Gardena Husqvarna
0 °C – 30 °C Room temperature 0 °C – 20 °C 5 °C – 30 °C 5 °C – 25 °C Up to +25 °C 5 °C – 25 °C

As can be seen from the table, all manufacturers recommend more or less the same storage conditions for battery packs based on Li-Ion cells.

Practical experience shows that lithium-ion batteries retain their capacity best when stored at 40% charge at around +5°C.

The design of a good Li-ion battery.

Specifics of Ni-Cd and Ni-Mh batteries

Nickel-cadmium (Ni-Cd) and nickel-metal hydride (Ni-Mh) batteries are slowly becoming outdated, although certain tools and equipment still use them.

  • It is better to store Ni-Cd batteries in a completely discharged state. The optimal temperature is about +10 °C. Before long-term storage, it is better to do 3 – 4 complete charging and discharging cycles.
  • Ni-Mh batteries should be charged halfway before short-term storage, and 100% before long-term storage. It is better to store it in a room where the temperature does not fall below 0 °C and does not rise above +20 °C (at higher temperatures the self-discharge rate of the battery increases significantly).

Conclusions

Proper storage of the battery during periods when tools and garden equipment are not in use is the key to battery longevity. By following the simple rules described in this article, the battery will last as long as it should (at least 500 to 1000 charging cycles or 3 to 6 years, depending on the brand and type of battery). Also keep in mind that only original chargers should be used to extend the life of the battery.