According to projections by the International Energy Agency
(IEA), there will be more than 200 million electric vehicles on the road by
2030. This development is being driven by rising consumer demand, the expansion
of charging infrastructure, and policies introduced by cities and governments
in support of electrification. Promoted as an environmentally friendly
alternative to combustion engines, electric vehicles do, however, have a weak
spot: the question of what happens to old EV batteries once they can no longer
store enough energy to power a vehicle.
Key Questions and Answers on Second Life for EV Batteries – At a Glance
What does “Second Life” mean for vehicle batteries?
Second life refers to the reuse of used batteries from electric vehicles for stationary
energy storage or other less demanding applications.
How is the condition of an old battery assessed?
The condition – or State of Health (SoH) – is determined using methods such as
open circuit voltage and impedance spectroscopy to evaluate remaining capacity
and performance.
Why is battery recycling expensive?
Recycling is costly due to the complex separation of materials and the lack of
standardisation in processing.
What are the benefits of a second-life programme?
Second life extends the total service life of batteries, reduces waste and
conserves resources by decreasing the need for newly produced batteries.
How are second-life batteries used?
They are typically used in stationary energy storage systems to store surplus
energy from renewable sources, or in low-demand applications such as e-bikes
and e-scooters.
Today, the
most common solution is reprocessing – in other words, recycling. Some
materials, such as cobalt and lithium, can be recovered, though by no means
all. However, recycling remains expensive, largely unregulated, and currently
lacks a clearly defined supply chain. Moreover, the Institute for Energy
Research estimates that by 2025, over 3.4 million used EV batteries will have
accumulated worldwide – a dramatic increase compared to just 55,000 in 2018.
Refurbishment gives EV Batteries a Second Life
An alternative to recycling is battery reuse. The first step
is to assess which cells in a battery pack can still store sufficient charge.
The pack is then dismantled and the usable cells are assembled into a new
battery. This approach – more precisely a transitional step rather than full
reprocessing – grants EV batteries a second life. Once a lithium-ion
battery’s capacity drops to around 70 to 80 per cent of its original level –
typically after eight to ten years – it can no longer reliably power a vehicle
and must be replaced. The growing number of spent batteries on the market
presents a new opportunity, now commonly referred to as second life.
Since the battery pack accounts for over 30 per cent of the
sale price of an electric vehicle, there are strong economic and environmental
incentives for battery manufacturers, automotive OEMs, regulators and even
insurers to support a secondary market. The most direct application is in
energy storage systems, where the still-functional cells from used packs can be
reused to store surplus energy from wind, solar, hydro or geothermal sources.
EV batteries can also be dismantled and repurposed into smaller battery modules
for less demanding uses – such as power tools, forklifts or e-scooters.
How the SoH of a battery is determined
The State of Health (SoH) of a battery refers to its
condition and ability to provide sufficient capacity. SoH describes the current
status of a battery in terms of performance and remaining service life.
To monitor and assess SoH, a variety of methods are used –
including internal diagnostics, external testing, and battery management
systems (BMS). Regular monitoring of battery condition helps to extend service
life and ensure reliable performance. Common methods for determining SoH
include:
- Open Circuit Voltage (OCV): Measures battery voltage when not under load. This value is compared to a table or algorithm to estimate the battery’s SoH.
- Impedance Spectroscopy: Measures the battery’s AC impedance at various frequencies to detect chemical changes that indicate a change in SoH.
- Calendar Age and Cycle Count: Batteries have a finite lifespan influenced by age and the number of charge-discharge cycles. Monitoring these factors helps estimate SoH.
- Coulomb Counting: Measures the charge entering and leaving the battery. Tracking this flow provides an estimate of the battery’s usable capacity and health.
Depending on the application and battery type, a combination
of these or other methods may be used to determine SoH. The State of Health can
be affected by factors such as age, usage duration, temperature, number of
charge cycles and type of application. A battery with a high SoH delivers good
performance and sufficient capacity, whereas one with low SoH may no longer
function reliably and must be replaced.
Why must the SoH be measured?
The State of Health (SoH) of batteries must be
measured before they can be used in second-life applications, to ensure they
still possess sufficient capacity for reliable operation in a new context. Here
are several reasons why SoH measurement is essential:
- Battery lifespan: Batteries have a finite service life and gradually lose capacity. SoH indicates how much capacity remains and how long the battery is likely to remain viable.
- Optimisation: SoH measurement allows for optimisation of the battery’s use in second-life applications. If enough capacity remains, the battery can be reused instead of being discarded.
- Safety: SoH is a crucial factor in ensuring safety. If a battery no longer holds sufficient capacity, it may not operate safely in a new application.
- Design: SoH data is essential for properly sizing and designing second-life systems. Without reliable SoH information, it is difficult to dimension such systems accurately.
- Diagnostics: SoH can be used diagnostically to monitor battery condition and determine whether it remains suitable for second-life deployment.
What’s the problem with measuring SoH?
In a word: standardisation — or rather, the lack thereof. Just
like in battery testing during manufacturing, there is currently no universal
standard for measuring SoH. For example, battery management systems (BMS) may
be either wired or wireless — just one of many variations. This lack of
uniformity means manual work is often required during disassembly, which makes
the process more expensive and remains a significant barrier to second-life
adoption for EV batteries.
One potential solution is designing batteries with
second-life use in mind, enabling easier disassembly. Standardised processes
could then be developed, including robotic support for dismantling and
repurposing.
What’s the difference between SoC and SoH?
State of Charge (SoC) and State of Health (SoH) are two
distinct parameters used to describe the condition of an EV battery.
What is “Second Life” in Vehicle Batteries?
Second life in vehicle batteries refers to the reuse of
batteries from electric vehicles that are no longer suitable for traction
purposes. While these batteries may not provide sufficient range for EVs, they
can still store usable energy for other applications.
Examples include:
- Stationary energy storage for buildings
- Power sources for low-demand vehicles such as e-bikes or e-scooters
Second-life use extends battery lifespan and conserves
resources by reducing the need to manufacture new units. However, these
batteries must be appropriately tested and assessed before reuse. The State of
Health (SoH) must be high enough to ensure performance and safety.
- SoC refers to the battery’s current level of charge. It is usually expressed as a percentage and indicates how much of the battery’s total capacity is presently available. A fully charged battery has an SoC of 100%, while a fully discharged battery reads 0%.
- SoH, by contrast, describes the long-term condition of the battery in terms of its performance and expected lifespan. It reflects how well the battery still functions relative to its original specification. A high SoH means the battery still performs well; a low SoH means reduced capacity and performance, and may indicate the need for replacement.
SoC is a snapshot that fluctuates during charging and
discharging, whereas SoH is a long-term indicator that changes gradually with
ageing and wear.
What are the advantages of wireless Battery Monitoring
Systems (BMS)?
The emerging market for second-life batteries is not without
technical, quality, and implementation challenges. For example, today’s EV
batteries usually rely on wired systems to monitor the state of charge. These
wiring harnesses often need to be removed before the battery can be reused,
adding cost and complexity to the design and dismantling process.
In line with the growing trend of designing products for
end-of-life disassembly, developers are increasingly turning to wireless BMS
(wBMS) concepts. Wireless battery monitoring systems help reduce the overall
size, weight, and material costs of electric vehicles. More importantly, they
enable robotic assembly and disassembly of battery packs, enhancing safety and
improving scalability for second-life industrial applications.
Battery Refurbishment
Wireless BMS technology allows for contactless, scalable
battery characterisation, facilitating quick decisions between reuse and
recycling. Once a decision is made using State of Health data – for example,
collected via wireless BMS solutions – buyers and sellers can establish a
standardised level of trust and fairly determine the value of a battery before
agreeing on a purchase price. The industry could even introduce a rating system
to distinguish between lightly used batteries rated "AAA" and heavily
degraded ones.
What to consider when buying an electric vehicle battery?
When purchasing an electric vehicle battery, users must
decide between new and used options. New batteries offer the latest technology
and maximum lifespan, but come at a higher price. Used batteries may offer a
more affordable alternative, but it is essential to carefully assess their
condition and remaining service life. A transparent history and certifications
confirming quality and safety are crucial. Reputable sellers should be able to
provide detailed information on the number of charge cycles and the current
health status of the battery.
Conclusion
The second-life use of EV batteries represents a valuable
intermediary step before recycling. However, its success strongly depends on
how holistically the battery’s first and second uses are considered. The design
of the battery and its management system must be geared towards the entire
service life. This may require both battery suppliers and automotive
manufacturers to rethink their approach. In the long term, though, they can
play a key role in building a sustainable and economically viable circular battery
economy.
This article was first published at all-electronics.de
The EU Battery2Life Project at a Glance
Funded by Horizon Europe, the Battery2Life project aims
to facilitate the transition of EV batteries into their second life. The consortium
is developing advanced battery management systems and optimised system designs
to enable reliable reconfiguration of used batteries, thus driving innovation
in Europe’s battery industry.
Two new system design frameworks are being developed:
- The first focuses on restructuring existing battery designs for second-life use.
- The second introduces new design principles that are applicable in both first- and second-life phases.
These concepts are being tested in Austria for home
energy storage systems, and in Greece for grid-scale storage applications.
Elisabeth Dörr, project manager at AIT, emphasises the
project’s significance:
“The outcomes of Battery2Life will support the transition to green energy and
positively impact both the European economy and the environment. Battery2Life
is a crucial step towards the sustainable use of EV batteries and supports the
development of a circular economy.” This is being achieved through the
implementation of wireless communication and the integration of
condition-monitoring sensors into existing battery modules.
