Retired EV Batteries to Power the Next Microgrid Boom?

An electric vehicle battery does not become useless when it can no longer deliver the range and power expected by a driver. In many cases, it still retains enough capacity for a less demanding job, including storing solar energy, reducing peak electricity demand, or providing backup power during an outage.

A new review published in the Journal of Energy Storage¹ examines how these second-life lithium-ion batteries could be integrated into microgrids. The researchers conclude that retired EV batteries can offer meaningful economic and environmental benefits, but only when their remaining health, safety, and performance are matched to an appropriate application.

This distinction is important. Second-life storage is not simply a matter of removing a battery from a vehicle and connecting it to a solar installation. It requires testing, classification, power conversion, thermal management, and continuous monitoring. The opportunity is therefore larger than battery reuse alone. It could create an infrastructure layer between automotive retirement and final recycling.

Why EV Batteries Are Retired Before They Are Exhausted

EV batteries are commonly retired from automotive service when their state of health falls to approximately 70% to 80% of their original capacity. At that point, reduced driving range and declining peak performance can make the battery unsuitable for a vehicle, even though it may remain capable of storing considerable energy.

Stationary systems operate under different constraints. A battery installed beside a building or solar array does not need to accelerate a vehicle, operate within a restricted weight allowance, or provide hundreds of kilometres of range. Size and weight matter much less, allowing batteries with reduced energy density to remain useful.

The review reports that second-life batteries can deliver energy efficiencies of 92% to 99%. Real-world deployments covered by the researchers reduced peak demand by as much as 60% and peak-time energy use by as much as 39%.

The available supply could also become substantial. The paper cites projections suggesting that retired EV batteries could provide approximately 96 GWh of second-life storage capacity by 2030 and as much as 3,000 GWh by 2040. This aligns with expectations that the number of retired batteries will rise sharply as the first large generations of EVs age.

The International Energy Agency expects around 14 million EV batteries to reach retirement in 2040. The question is whether those batteries should immediately be dismantled for materials or used for several more years before recycling.

Matching Each Battery to the Right Microgrid

The paper’s most useful contribution is a proposed grading framework that assigns batteries to different microgrid applications. Rather than treating every retired pack as interchangeable, the system evaluates health, degradation, thermal behaviour, remaining life, cell imbalance, operational stress, cost, and efficiency.

Batteries receive the lowest grade triggered by any individual measurement. If a pack performs well in eight categories but fails the thermal-safety requirement, it is removed from the second-life pool. This conservative approach recognizes that an energy-storage system is only as dependable as its weakest critical component.

This cascading model could improve the economics of the battery lifecycle. Stronger batteries would be reserved for applications requiring rapid responses and frequent cycling. Weaker but still serviceable units could handle occasional backup duty. Batteries falling below minimum safety or performance thresholds would proceed to recycling.

There is an important commercial implication hidden in these thresholds. Grade A requires at least 80% state of health, which is also near the point when many EV batteries are retired. This means only a portion of retired packs may qualify for the most valuable grid services. Access to battery history, module-level testing, and automated sorting will determine how much usable inventory a repurposer can recover.

The Economics Depend on Acquisition and Processing Costs

The review finds that second-life batteries become especially attractive when their acquisition cost falls below approximately 40% of the price of a new battery. Under favourable conditions, studies included in the review reported storage-cost reductions of 13% to 40%, internal rates of return above 41%, and net-present-value improvements approaching 49.2%.

Frequency regulation, where batteries rapidly balance fluctuations in electricity supply and demand, emerged as one of the most profitable applications. Other promising uses include:

• Storing excess solar and wind generation
• Reducing commercial peak-demand charges
• Supporting EV charging infrastructure
• Providing backup power to isolated microgrids

However, low battery prices do not automatically produce an inexpensive storage system. Collection, transportation, testing, disassembly, module matching, new enclosures, inverters, cooling systems, certification, and warranties all add costs. Cell-level disassembly can become uneconomical because of its labour intensity, while processing batteries at the pack or module level may offer better margins.

Falling prices for new batteries create another challenge. According to the IEA’s 2026 battery-market assessment, used EV battery prices have declined, potentially creating more opportunities for reuse. At the same time, inexpensive new lithium iron phosphate batteries raise the performance and warranty standard that second-life systems must beat.

The relevant metric is therefore not the initial battery price. It is the complete cost per unit of energy delivered over the system’s remaining life.

Battery Data Could Become More Valuable Than Battery Ownership

The largest obstacle may be uncertainty rather than degradation itself. Two batteries showing 75% remaining capacity may have experienced entirely different operating histories. One may have accumulated gradual highway mileage in a moderate climate, while another endured rapid charging, deep cycling, or repeated exposure to high temperatures.

Without reliable history, repurposers must conduct extensive testing to estimate state of health and remaining useful life. This creates a strong case for digital battery passports that preserve information about chemistry, charging patterns, temperature exposure, repairs, and ownership throughout a battery’s first life.

Better data would support several improvements:

Automated grading could become faster and less expensive. Insurers could price risk using observed battery histories. System integrators could offer more credible warranties. Microgrid controllers could adjust charging behaviour according to the health of individual modules rather than treating the entire installation as a uniform battery.

This may shift the industry’s competitive advantage. Owning a large inventory of retired batteries is useful, but knowing which batteries are safe, how they will degrade, and where they should be deployed could be more valuable. Previous Securities.io coverage has similarly examined the growing second-hand battery market and the role of repurposing in extending battery value.

Safety and Standardization Remain the Bottlenecks

The paper identifies thermal runaway as the dominant safety concern. Aging cells can develop different capacities and internal resistance levels, causing individual modules to heat and discharge unevenly. Fixed limits designed for new batteries may not adequately reflect these changing conditions.

More than 20 standards address portions of battery testing and safety, yet the researchers found no universal framework covering the complete journey from EV retirement through microgrid deployment. The proposed grading system is an attempt to connect those fragmented requirements, but it remains a literature-derived framework rather than a standard validated across large commercial fleets.

Wider adoption will require shared testing procedures, clear liability rules, interoperable battery-management systems, and certification processes recognized by insurers and regulators. Until those elements mature, second-life projects may remain concentrated among experienced integrators capable of managing the additional technical risk.

Investing in the Infrastructure Behind Second-Life Storage

For investors, the more dependable opportunity may sit around the battery rather than inside it. Repurposed storage requires inverters, switchgear, thermal controls, monitoring equipment, microgrid software, and engineering services regardless of which vehicle originally supplied the cells.

Eaton Corporation provides relevant exposure to this enabling infrastructure. The company develops microgrid controllers, electrical-distribution equipment, power-conversion systems, energy-management technology, and integration services. It has also participated in a European second-life battery demonstrator referenced by the review.

This makes Eaton a more direct fit than an automaker that merely produces a future supply of retired batteries. Its opportunity is to provide the equipment and intelligence that allow heterogeneous energy assets to operate as a dependable system. Second-life batteries are not currently a central driver of Eaton’s business, but growth in microgrids, distributed storage, and electrification could expand demand for the company’s broader power-management portfolio.

Investors should still distinguish between sector exposure and a pure-play investment. Eaton participates across data centres, buildings, utilities, aerospace, vehicles, and industrial markets. Second-life storage represents one possible beneficiary of its microgrid capabilities rather than a standalone investment thesis.

Giving Batteries a Second Job Before Recycling

Recycling remains the final destination for lithium-ion batteries, but it does not always need to be the immediate one. A battery that no longer meets automotive requirements may still provide years of stationary service before its materials are recovered.

The review suggests that second-life batteries can lower storage costs, reduce lifecycle emissions, support renewable generation, and improve energy access. Its more important message is that those benefits depend on selecting the right battery for the right job.

If battery passports, automated diagnostics, safety standards, and health-aware control systems mature together, retired EV packs could become a significant source of distributed storage. The resulting market would not merely extend battery life. It would create a new link between transportation, energy infrastructure, and the circular economy.

References:

¹ Suri, V., Dhundhara, S., Guéniat, F., & Sharma, R. (2026). Second-life lithium-ion batteries for microgrids: A comprehensive review of integration, degradation, control, and reliability. Journal of Energy Storage, 181, 124330. https://doi.org/10.1016/j.est.2026.124330