Calendar ageing refers to the ageing process that takes place regardless of whether a battery is used or not. It is important to keep in mind that a battery also ages during storage and can no longer be considered “new” after some time, even if it is in its unopened packaging. Chemical processes take place within them that can affect their health, their capacity and ultimately, above all, their safety.

Differentiation from cyclical and erratic ageing

Calendar ageing should not be confused with the cyclical ageing of batteries caused by charging and discharging. In addition, there are sudden ageing phenomena, e.g. due to extreme temperature fluctuations or physical effects on the battery.

In summary, this means that a battery — like a human being — ages of its own accord. The more frequently and intensively it is used, the more this process intensifies.

How does storage affect the ageing of batteries?

Good storage conditions definitely have a positive effect on the ageing process of batteries. They are also a safety factor. Above all, it is important to protect the batteries from moisture and extreme temperature fluctuations. Although calendar ageing still progresses, the risk of sudden ageing is minimized. It is best to store batteries in a cool and dry place that is explicitly approved for this purpose.

How does calendar ageing make itself felt in everyday life?

The ageing process of batteries can therefore not be prevented. It is noticeable in everyday life through various factors:

Self-discharge: The self-discharge process becomes increasingly stronger as time goes on and causes the battery to lose its charge increasingly quickly.

Decrease in capacity: The older the battery gets, the less energy it can store and release.

Increased internal resistance: As a battery ages, its internal resistance increases, causing the battery to lose voltage more quickly under load and reducing its efficiency.

Changed voltage level: Older batteries can no longer maintain a stable charge. This has an impact on the reliability of the devices in which they are used.

Changed charging and discharging times: The calendar ageing of batteries can also be noticeable in that the battery charges and discharges faster. Some battery management systems compensate for this with lower charging currents so that longer charging times are possible. If this is the case with older batteries, this indicates a good battery management system.

How can I determine how much a battery has aged?

Companies often have to deal with batteries that they know very little about. More important than the question of how old a battery actually is, it is important to know what the state of health and capacity of the battery is. This is the only way to determine the residual value of the battery and establish whether it is still suitable for a planned Second Life application, for example.

The age of a battery alone says nothing. Never assume that the condition of one battery is the same as that of another battery of the same age. Two batteries can be produced in the same company on the same day and still be in a completely different state of health.

We therefore recommend always testing batteries — and individual battery cells if necessary — with the Battery Analyzer or Cell Analyzer and having them monitored by our AI during use, especially in battery storage systems.