When an electric car battery reaches the end of its first life, it faces a choice. It can be recycled for its materials, or it can start a second career storing energy. Most people assume reuse is always the greener option. New CIRCUBATT research suggests the answer depends on something far less obvious: the electricity grid the battery plugs into.
Our public Environmental and Economic Impact Report compares recycling and reuse for two common battery chemistries in two very different countries, France and Poland. Its findings show that the battery reuse carbon footprint can change dramatically from one country to the next, even when the battery is exactly the same.
What does a second life battery actually emit?
A battery in stationary storage does not burn fuel. However, every time it charges and discharges, a small share of the energy turns into heat and is lost. In the CIRCUBATT analysis, that loss is about 1.6% per cycle for NMC811 cells and 1.9% for LFP cells.
Someone has to generate that lost electricity. Its climate impact therefore depends on how clean the local grid is. Experts measure this as grid carbon intensity: the grams of CO2 emitted for every kilowatt hour of electricity.
Same battery, different grid
The two countries in the study could hardly be more different. In 2024, nuclear power supplied about 68% of France’s electricity, while coal supplied about 54% of Poland’s. As a result, the Polish grid emits about 719 g of CO2 per kWh, compared with about 51 g in France.
That gap is about fourteen fold, and it carries straight through to the results. A second life battery operating in Poland causes about 14 times more emissions from energy losses than the same battery in France. The report’s conclusion is clear: in low carbon markets, reuse brings clear environmental benefits and should be encouraged. In high carbon grids, the environmental case becomes much harder to make.
Cheaper recycling is not always cleaner recycling
The same pattern appears in recycling. Our companion Cost Optimisation Analysis found that recycling is more profitable in Poland than in France, mainly because labour, electricity and gas cost less there.
The climate picture points the other way. For direct recycling at pack level, emissions in France are roughly 45% lower for NMC811 and about 51% lower for LFP. In other words, the cheapest place to recycle a battery is not automatically the cleanest. The report sums it up simply: cost and CO2 are very independent factors in battery recycling.
This matters for anyone deciding where Europe should build its recycling plants. If the industry follows cost alone, it could end up locating capacity where the climate benefit is smallest. We explored the economic side in more depth in Why Battery Recycling Isn’t Profitable Yet in Europe.
Battery chemistry changes the answer
Chemistry adds another twist. LFP batteries last much longer in second life than NMC811 batteries. Because they run for more cycles, they also lose more energy over their lifetime. Consequently, their cumulative emissions come out roughly 2.3 to 2.5 times higher.
That does not make LFP the worse choice. It simply reflects a longer working life. In fact, the cost analysis found that LFP reuse is profitable in nearly all modelled scenarios, while NMC811 reuse is unprofitable in almost all of them. Recycling reverses the ranking. NMC811 is more profitable to recycle, because it contains more valuable metals such as nickel and cobalt.
Put together, these findings point to a practical rule of thumb. The best end of life route depends on both the chemistry and the location, so a one size fits all strategy is unlikely to work.
Working harder does not help
The analysis also tested whether running a second life battery twice a day changes the climate result. It does not. Two cycles a day simply use up the battery’s life faster, so total emissions end up almost identical to one cycle a day.
What the battery reuse carbon footprint numbers do not show yet
These results come with an important caveat. The analysis only counts emissions from energy lost during charging and discharging. It does not yet include the emissions a storage battery can help avoid, for example by storing solar and wind power and releasing it later.
That benefit could be significant, especially in grids that still rely on fossil fuels. CIRCUBATT will model these avoided emissions in its next deliverable. The current figures are therefore best read as one half of the picture, not the final verdict on reuse. If you want to know how well second life batteries actually perform, read Second Life Batteries: Do They Really Perform Poorly?.
See the findings in Lyon
From 16 to 18 November, CIRCUBATT will present these results in a poster titled “Recycle or Reuse?” at Batteries Event 2026 in Lyon. If you are attending, come and find us in the poster area.
Recycle or reuse is rarely a yes or no question. The right answer depends on what the battery is made of and where it lives. Want to learn more about the project? Visit our frequently asked questions.