Millions of Old EV Batteries Could Get a Second Life Helping Power The Grid

Retired EV batteries may help solve the grid’s storage problem.

Retired EV batteries are starting to get a second job: helping keep the lights on.

A battery that can no longer push a car hundreds of miles may still have years of life left. Instead of sending it straight to recycling, companies are packing used EV batteries into grid storage systems that can soak up solar power by day and release it when demand rises.

The shift is arriving just as two problems collide. Millions of aging EV batteries are approaching retirement, and power grids need more storage to handle the surge in wind and solar energy. In 2025, global electric car sales topped 20 million, according to the International Energy Agency, so in 8 to 12 years, you’ll have that many battery packs that could be linked together to store renewable energy rather than get discarded. In the United States, developers have begun work on a number of such stations this year. According to the U.S. Energy Information Administration, developers plan to add 24 gigawatts of utility-scale battery storage in 2026, after a record 15 gigawatts in 2025.

For an old EV pack, the road may be over. The grid may be just beginning.

The Battery’s Second Act

June brought several signs that second-life batteries are moving beyond demonstration projects. According to IEEE Spectrum, B2U Storage Solutions said it would repurpose used batteries from Waymo robotaxis for grid storage. Redwood Materials announced a project using about 100 General Motors batteries to provide 1.5 megawatts to a GM plant in Michigan. Moment Energy completed what it called the world’s largest EV battery repurposing facility.

The appeal is both environmental and economic. Recycling recovers some of the lithium, nickel, cobalt and copper that went into the battery’s manufacturing, at varying costs. But repurposing can extract more useful work from batteries before they are broken down. A July 2025 ACEEE policy brief argues that second-life storage can reduce greenhouse gas emissions, cut demand for new mining and offer lower-cost backup power, especially for communities that face high energy burdens.

This confidence “was not there three or four years ago,” Simona Onori, a professor of energy science and engineering at Stanford University, told IEEE Spectrum. “Batteries retired with 70 to 80 percent of their original capacity . . . can be excellent candidates for grid storage,” she added.

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A used EV battery is not ideal for every job. It works best when it does not have to charge and discharge constantly. That makes it a good fit for backup power at businesses, where the battery may sit ready for an outage and only run occasionally. It can also work for some grid storage or EV charging stations, depending on how often the system is used. But it is a poor fit for jobs that demand rapid, repeated charging and discharging all day, such as helping the grid balance tiny second-by-second changes in electricity supply and demand. Those tasks wear batteries out faster, and second-life batteries have already done years of work in cars.

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Not All Batteries Had the Same Life

“Two battery packs that are the same age can have very different states of health depending on their depth of discharge history, fast charging frequency, and temperature exposure in their EV life,” Anurag Srivastava, a professor of electrical engineering at West Virginia University, told IEEE Spectrum.

Repurposers need to know how much capacity remains, how much internal resistance has built up, whether cells behave consistently and whether the pack has suffered heat, damage or abnormal degradation. For instance, B2U follows UL 1974, a safety standard for repurposing batteries. The company groups similar batteries in container-sized cabinets and lets weaker packs disconnect when they reach voltage limits.

“The weaker batteries will hit their upper voltage limits earlier, and then they can disconnect and not inhibit the stronger batteries from reaching their higher voltage limit,” Hall said. “There’s a lot of software required to do that well.”

Then comes the software. Modern EV batteries carry a battery management system, or BMS, that tracks voltage, temperature, charging history and faults. But automakers often treat that data as proprietary. This is why the ACEEE brief identifies data access as perhaps the central bottleneck for the industry. Without it, companies must spend more time and money testing packs, or reverse-engineer systems designed for cars rather than the grid.

The Race Against Cheaper New Batteries

Second-life batteries face a moving target: new batteries keep getting cheaper. BloombergNEF reported that stationary storage pack prices fell to $70 per kilowatt-hour in 2025, 45 percent lower than in 2024. That makes it harder for used batteries to win on price once testing, transport, certification and integration are included.

A lot may also depend on the type of battery once used in EVs. Nickel-manganese-cobalt batteries contain valuable metals, so recyclers may pay more for them. Lithium iron phosphate batteries, or LFP batteries, use cheaper materials, carry lower fire risk and often offer less value to recyclers, making them better candidates for repurposing.

Policy could decide how much of this market grows. The European Union will require a digital battery passport starting in 2027, making batteries one of the first product groups to carry mandatory lifecycle data. Analysts say that kind of transparency could help reuse, repair, repurposing and recycling.

For now, second-life EV batteries remain a small slice of the storage market. But the wave is coming. The first mass-market EVs are aging out. Newer fleets will follow.