Charging lithium-ion batteries

summary: charging a Lithium-ion battery

• Charge STIHL lithium-ion batteries to 80-100% before using them for the first time

• Safety technologies prevent lithium-ion batteries from overheating

• Overnight charging of a lithium-ion battery is safe

• Protect lithium-ion batteries from moisture, heat and cold

What to be aware of when charging lithium-ion batteries

The assumption that batteries need to be fully charged after purchase no longer applies to advanced lithium-ion batteries. However, there are a few things you should keep in mind to ensure that your batteries have a long service life.

Ideal temperature for charging for lithium-ion batteries 

Your STIHL Li-ion battery can be charged without a problem at temperatures between 5°C and 40°C. STIHL lithium-ion battery chargers also incorporate safety features so that if your battery is too hot when inserted into the charger after a long period of use, the charging process will only begin when it falls to an appropriate temperature.

Avoid extreme temperatures when charging lithium-ion batteries

When charging, your Lithium-ion battery should not be placed on a heater. Warming a charging battery does not save battery life and does not increase the capacity – in fact, the battery may be damaged if temperatures are too high or too low. Your Li-ion battery is best charged at normal room temperature or at moderate outdoor temperatures. We advise that you always check your battery’s permissible temperature range.

Long charging processes are not required for lithium-ion batteries

Advanced lithium-ion batteries only require 80% charge before their first use – this takes between half an hour and four and a half hours, depending on the battery.

Does the temperature of a battery affect the amount of energy it provides?

One myth suggests that a battery should be placed on a heater during charging. This theory is based on the idea that electrical activity will increase as a result of the heat input, which should protect the battery during charging and extend its service life.  Some claim it should even be possible to briefly reactivate a fully flat battery by heating it, on the grounds that only a warm battery can access its entire energy reserve. Now we know that not only is this theory incorrect, but the process is actually harmful to the battery.

During charging and discharging, ions move from one battery electrode to the other, depending on the direction of flow. If the battery is made too hot by the process, the particles accelerate and the material breaks down, leading to reduced battery life. If the battery overheats, in a worst-case scenario highly flammable gases may be released meaning that the battery becomes unusable. 

We advise that you always check your battery’s permissible temperature range.

How dangerous is it to charge a battery for too long?

It's normal for a battery to warm up during charging, and is not a cause for concern. STIHL batteries are protected against overheating and are basically risk-free. When a battery reaches its full charging capacity, the charging process stops and the current is switched off. This prevents overcharging and the associated heat build-up.

If a battery exceeds its approved temperature range, it can cause a self-reinforcing exothermic chemical reaction called a “thermal runaway”. The heat generation within the battery becomes self-reinforcing, sparking a circular chain reaction which quickly melts the battery core. 

It is true that the risk of battery fire continues to be a matter of concern for many users. However, advanced STIHL batteries keep you on the safe side.

What advantages do products with lithium-ion batteries from STIHL offer?

STIHL uses high-tech lithium-ion cells in all its cordless products. This technology has many advantages, including low risk of fire from lithium-ion batteries, optimal protection against deep discharge, and temperature monitoring by means of an efficient battery management system. 

The highest safety standards for STIHL lithium-ion batteries

To prevent overcharging and excessive heat development, only lithium-ion cells that meet the highest safety requirements are installed in STIHL batteries. Both batteries and chargers from STIHL are fitted with protective mechanisms that prevent overcharging and excessive heat generation.

Temperature monitoring by means of a battery management system

Each individual cell installed in a battery is monitored by a battery management system. This involves an integrated sensor which measures the temperature at the warmest point inside the battery – if the temperature is too high, the charging process is interrupted. 

Low fire hazard with lithium-ion batteries

With advanced lithium-ion batteries, the risk of fire is very low. This is ensured through various measures, one of which is the built-in battery management system that prevents overcharging and the associated high heat generation.

Optimum protection against deep discharge

The electronics in lithium-ion batteries automatically put batteries into an idle state if they are not used for a long period of time. This protects against damaging deep discharge.

Only low capacity loss

All STIHL cordless products use advanced lithium-ion cells which do not need to be fully charged before first use and are ready for use within a few hours. In a year, a STIHL Li-ion battery loses just 1-3% of capacity via self-discharge.

No memory effect

The memory effect describes the permanent loss of capacity that nickel cadmium batteries are affected by. Repeated partial charging reduces the amount of power the battery makes available, as it only “remembers” the most recently added amount of energy, rather than its full capacity. The advent of the Li-ion battery means this issue with partial charging is a thing of the past.

For optimum storage of our lithium-ion batteries, we recommend an ambient temperature of around 20 degrees. In principle you can store the batteries between -20 and +50 degrees – however, there may be a loss of function and service life at the top and bottom of this range. That’s why we recommend storing lithium-ion batteries correctly.

STIHL battery charge indicator

The four LEDs on a STIHL Li-ion battery communicate the charge level, but can also indicate a malfunction on the power tool or battery. Press the button on the battery and the LEDs will light up green for around five seconds, then indicate the charge level. If only one LED flashes green, the battery level is low.

The green LEDs also indicate the charge level while the Li-ion battery is charging (if no LEDs are lit, the charging process is complete). If the LEDs are lit up or flashing red during charging, a malfunction has occurred.

^{The LED display of the battery provides information about the charge level or faults.}