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What Factors Impact the Aging Process of Batteries?

What Factors Impact the Aging Process of Batteries?
A battery being manipulated inside the car

Batteries undergo calendar aging as they age over time due to internal chemical reactions, which gradually degrade the materials within, thereby diminishing the battery’s capacity. The rate at which these reactions occur, or the rate of aging, is influenced by various factors such as temperature, state of charge (SOC), and depth of charge/discharge cycles.

This article is intended to shed light on:

  • which factors influence the aging process in a battery
  • what can be done to slow down battery aging.

Which factors impact a battery’s aging process?

It is essential to understand that all batteries age over time, a process called calendar aging. Calendar aging is a process that affects batteries, mainly when they are not in use or are stored for extended periods.

By acknowledging that all batteries age over time, users can make informed decisions, optimize battery usage, and take proactive measures to mitigate the impact of aging on battery performance, safety, and cost.

  • The rate of these reactions, or rate of aging, depends on several factors, including temperature, state of charge, and the number and depth of charge and discharge cycles.
  • A battery’s lifespan can vary depending on its performance and the cumulative effects of aging under different conditions.

Six battery packs are visible in the back of an E-Bus as the case is opened, revealing its connections. Multiple battery packs inside an E-Bus. Spielvogel (2014)

High Temperatures

The ideal temperature for any battery is room temperature, so about 25°C/77°F. Usually, this temperature is also specified in the manufacturer’s data sheets.

  • Operating at higher temperatures, especially near the maximum allowable limit, will increase the aging rate.
  • The aging factor value represents the time in hours elapsed at a temperature higher than the ambient temperature, with the index increasing as the temperature rises.

A man opening the cover of four E-Bus battery packs to check them. E-Bus battery packs being checked. Heavy Duty Slide (2019)

Factors that Impact Battery Aging

State of Charge (SOC)

The “ideal” or optimal State of Charge (SOC) for a lithium-ion battery is 50% because this is when the electrochemical processes within the battery are most stable.

The battery ages faster as the SOC moves away from this midpoint.

The most significant impact on SOC aging occurs when a fully charged battery voltage is maintained above its natural resting voltage after charging is complete.

Resting voltage indicates battery charge but is not a direct measure of SOC. This is mainly determined using techniques like voltage and current measurements or estimations based on the battery’s discharge curve. Resting voltage is one factor considered in deciding SOC.

A top view of different components from an E-Bus, including battery packs. E-Bus component overview. Heavy Duty Slide (2019)


Taking everything into consideration that you have learned this week, it is safe to say that there are several reasons why batteries are aging. The most common ones are: usage, time, high temperatures, degrading materials, and state of charge.

Knowing and understanding a battery’s state of health (SOC) and its end of life (EOL) is essential for working with batteries and EVs and integrating new technologies, e.g., innovative sustainable transport.

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