Ageing - SoH loss

General

NMC811 batteries (Nickel 80 % - Manganese 10 % - Cobalt 10 %) are the most common batteries for e-bikes. They age through storage (calendar) and use (cyclical).

• SoH (State of Health):
  This is the net capacity in [%] of a battery after deduction of the two ageing processes.
• Calendar aging:
  Calendar ageing refers to the ageing of the battery while it is stored on the shelf and not in use. Among other things, it depends on the cell type, chemistry, storage temperature and state of charge (SoC). It is non-linear. The swarm knowledge in the WWW gives values of 0.5 -3% capacity loss/year (depending on the storage conditions, especially the temperature). Even with optimum storage, the battery deteriorates.
• Cyclical aging:
  Cyclic ageing occurs due to repeated charging and discharging cycles of a battery. Each cycle leads to chemical reactions that impair the performance of the battery over time. The charging management (incl. recuperation) but also the discharge currents, the operating temperature, the C-rate and the DoD are decisive parameters. It is not possible to give a general percentage as there are too many factors involved.

Conclusion

Every NMC-811 battery loses capacity continuously from the time of manufacture - both on the time axis through storage and through use. Exact values depend on the individual conditions.

A good introduction to the topic is, for example, to read 'Optimized Aging Behavior of Battery Modules - mediaTUM'. See also my compendium: 'The Li-ion battery | theory and concept compendium'.

Stromer and the SoH!

With the new version of the Omni app (4.0.5 (2252)) from August 2025, the SoH can be viewed on the start page. For more information see here.

Own experience

I measured the SoH loss of my BQ983 battery over a period of around three years.

Measuring arrangement:
Battery: BQ983 (blue), new
Stromer: ST3
Measurement period: Aug. 2019 to Oct. 2022

The battery was used in both winter and summer. The charging stroke (DoD = Depth of Discharge) was usually 70-100 % and could not be optimized due to the commuting distance, i.e. the battery was always fully charged and usually run down to an SoC of 30% to 0 %. The Stromer was driven at 90 % with 'All In'.

Evaluation from forums

To get an idea of the development of the SoH, I also analyzed 48 feedbacks from various Stromer forums and Facebook groups. I have not included nine SoH values (from 10,000 km with SoH > 95 % and without extender battery) as they are not realistic due to the cyclical and calendar degradation of a Li-ion battery.

The following statement can be derived from the statistics on SoH loss or the 'guarantee range': 

A Stromer battery can reach the 75 % SoH threshold from approx. 16,000 km. The average is approx. 22,000 km.

Roughly speaking, you can assume a loss of around 1% SoH / 1,000 km.

As the diagram shows, there are outliers on both sides. The dispersion is quite large and is probably related to the way the battery is driven or handled.

Slow down ageing

Positive factors for slowing down the ageing process include

• Limitation of the loading stroke
• Correct charging: Not in the cold or after a long drive in the hot summer
• Avoid recuperation level 4-5 over a longer period of time
• Don't leave electric cars in the sun any longer
• Using a Extender batteries

Storage etc.

> See AKKU - 'Self-discharge of a BQ983 battery'
> See AKKU - 'Extend service life?!
> See AKKU - 'Care: Mechanical / in operation / storage / safety'