Second life for lithium batteries

Second life means putting lithium battery modules into a different function, almost always stationary storage, when they no longer serve their original application but still hold between 65% and 80% of their state of health (SOH). If the battery returns to the same function, the job is refurbishment; if it changes function, it is second life (repurposing), which we also call revalorization. EcoBaterías tests and matches the modules and delivers them with a per-module report and a measured usable-energy label; below 65% the battery goes to recycling.

Thresholds and times: EcoBaterías test protocol, published in lithium battery testing · September 26, 2026.

What is second life, and what is it not?

A lithium battery stops serving its original application long before it runs out of energy. An electric vehicle pack is retired when it no longer delivers the promised range; a storage rack is retired when it no longer meets the power contract. In both cases usable energy remains, but under conditions harsher than those of a calm stationary application.

Second life is not repair or refurbishment. Repair fixes a specific fault, such as the BMS, a contactor or a weak module, and refurbishment tests every cell and replaces the weak ones. In both cases the battery returns to the same use, and it makes sense while the state of health stays above 80%. Second life is not recycling either: recycling recovers the materials of the cell, and it is the route when no usable energy is left.

Second life is a middle ground with its own rules: the module changes owner, application and duty cycle, so it needs a new measurement, new matching and a new label. A module that arrives untested and is installed “as is” is not second life: it is an electrical and thermal risk moved somewhere else.

The EU Battery Regulation calls this change of function “repurposing”: using a battery that is not waste for a purpose different from the original one (Regulation (EU) 2023/1542, Article 3(31)). IEC 63330-1:2024 treats “second use” and “second life” as equivalent terms. In Chile, Ley REP (Law No. 20,920, Chile’s Extended Producer Responsibility law) calls the set of actions that recover waste “valorization”, and valorization includes preparation for reuse and recycling (Article 3 No. 30).

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Sources: state-of-health thresholds from the EcoBaterías test protocol · Regulation (EU) 2023/1542, Article 3 (opens in a new tab) · Law 20,920, Article 3 (opens in a new tab) · September 26, 2026.

When does a module qualify? The SOH thresholds

State of health (SOH) is the module’s current usable energy as a percentage of its energy when new. We do not take it from the value the BMS declares: we measure it with an instrumented charge and discharge cycle and cross-check it against internal resistance and 24-hour self-discharge.

If the batch comes from a storage system and you have an export from its BMS, the LifetimeBESS battery health score (opens in a new tab) gives a first reading before you send us the batch; the second-life grading always comes from our own measurement.

Our second-life threshold is the 65–80% band, and it is our own threshold, not a standard. Above 80% the module still performs in its original application and is better repaired or refurbished than moved to a lesser use. Below 65% the remaining energy no longer covers the cost of dismantling, testing, matching, structure, electronics and warranty: at that point the value is in the minerals, not the electrons.

As a reference, a grading used in the industry keeps demanding uses above 80%, stationary storage and backup between 50% and 80%, and recycling below 50%. Our band is narrower because a second-life block has to last long enough to pay for its integration.

On top of the capacity measurement we apply three filters that rule modules out whatever their SOH: visible mechanical damage, a history of thermal events or swelling, and excessive spread between cells within the same module. A module at 74% SOH with one weak cell does not go into a second-life block; it goes to recycling.

Source of the reference grading: Zhang et al., arXiv, 2025 (opens in a new tab).

How are modules matched?

The life of a second-life block is set by its weakest module. That is why matching is the step that most determines the result, and it is done with measured data, not with the serial number or the vehicle’s year.

1. Grouping by chemistry and formatLFP with LFP, NMC with NMC, same cell format and same module architecture. Chemistries are never mixed within a block.
2. Capacity bandModules whose measured capacity falls within a narrow band are grouped together; outliers are moved to another block or sent to recycling.
3. Internal resistanceDC and 1 kHz resistance are compared; a high-resistance module runs hotter and drags the rest down even if its capacity looks right.
4. Self-dischargeThe resting voltage drop over 24 hours is measured. A module with abnormal self-discharge is discarded: it is the defect you see least and that causes most trouble later.
5. Cycle and thermal historyCycle count, peak recorded temperature and insulation events are read from the BMS and documented in the block record.
6. Labeling and traceability recordEach module gets a unique code and each block its measured usable energy, test date and retest plan.

Reference standards: IEC 63330-1 and UL 1974

We work with international references for preparing batteries for a use different from the original one:

• IEC 63330-1:2024, Repurposing of secondary batteries – Part 1: General requirements: sets the procedure to assess the performance and safety of used lithium-ion cells, modules and packs moving to another application, with traceable data.
• ANSI/CAN/UL 1974:2023 (2nd edition), Evaluation for Repurposing or Remanufacturing Batteries: requires reviewing the history and BMS data, inspecting, and measuring voltage, insulation, capacity, internal resistance and self-discharge before grading, with a grading system of 6 sigma or tighter.
• IEC 62933-5-3:2023, safety requirements for grid-integrated storage systems that undergo unplanned modifications, including the installation of reused or repurposed batteries.

In the United States, the NFPA 855 installation standard only accepts electric vehicle batteries in a storage system if they are repurposed by a company that complies with UL 1974. We cite these as reference standards for our method. They are not an EcoBaterías certification and we do not present them as one: what we deliver is the test report with the measured data, so the designer or the auditor can verify it independently.

Sources: IEC 63330-1:2024 (opens in a new tab) · UL Solutions, UL 1974:2023 overview (opens in a new tab) · IEC 62933-5-3:2023 (opens in a new tab)

A second-life battery without a per-module test report is not a second-life battery: it is a used battery.

What does the SEC require to connect a second-life system?

A storage system connected to the grid or to a building installation is, first of all, an electrical installation. Technical instruction RGR No. 06/2024 of Chile’s electricity and fuels regulator (Superintendencia de Electricidad y Combustibles, SEC) requires lithium-ion batteries and their BMS to meet IEC 62619, UL 1973 or UL 9540, with those documents attached to the declaration. The instruction does not mention used, refurbished or second-life batteries: that is the real barrier today for connecting a second-life block, and it is worth checking with the SEC before designing the project.

The same instruction limits lithium systems inside homes to 20 kWh, outside bedrooms, bathrooms, kitchens and attics. Above 20 kWh it requires a closed room, smoke detection and an extinguisher that does not react with the battery chemistry.

Declaring the installation to the SEC is up to the owner and their licensed electrical installer; EcoBaterías does not take part in that procedure. What we do deliver is the technical information the designer needs: measured usable energy per block, maximum voltage and current, internal resistance, temperature limits, cycle history and recommended operating conditions.

Source: SEC, technical instruction RGR No. 06/2024 (opens in a new tab).

Realistic applications in Chile

Second life pays off where the required power is moderate, cycles are predictable and space is not critical. In Chile, it fits cases like these:

• Backup for remote mining sites and camps, where backup today is a diesel generator that runs a few hours a day.
• Solar self-consumption in industry and retail, to shift midday energy to the evening peak.
• Backup for low-power critical systems: telecommunications, controls, emergency lighting, pumping.
• Fleet workshops and depots, to smooth the charging peak of electric vehicles without upgrading the grid connection.
• Community and rural electrification projects, where the cost of new storage is the main barrier.

We do not recommend second life for fast-response grid services or for applications that demand sustained high power: there degradation speeds up and the cost advantage disappears.

Lifetime, warranty and follow-up

We do not publish a lifetime in years, because it would depend on a duty cycle we do not control. We publish what we do measure: usable energy at handover, spread within the block and the internal resistance curve. On that basis, the contract sets the warranty by available energy and by period, together with a retest plan.

Retesting is part of the service, not an extra: a second-life block is measured again to confirm that the matching holds. When the block drops below the agreed threshold, it is withdrawn and goes to recycling: we manage its valorization with authorized receiving facilities, in Chile or in OECD countries where applicable; the authorized receiving facility closes the SIDREP declaration (Chile’s national hazardous-waste declaration and tracking system) and issues the valorization certificate. The loop closes without the owner having to find a new waste manager. Details in lithium battery recycling for companies.

Does second life count toward Chile’s EPR law?

Law 20,920 requires producers to collect and recover the priority products they place on the market, and batteries are among them (Article 10). Batteries do not yet have their own targets decree: the Ministry of the Environment published a draft through Res. Ex. 821/2026 and its deadline to propose the decree is January 29, 2027.

That draft matters for second life for one concrete reason: it proposes that at least 30% of the lithium-ion target be met through preparation for reuse, not through recycling. If the text holds, grading and reusing modules stops being a voluntary alternative and becomes part of compliance. Until then, we describe it as what it is: a proposal under consultation.

Source: Ministry of the Environment, draft supreme decree on batteries (Res. Ex. 821/2026) (opens in a new tab) · September 26, 2026. Framework in force: Law 20,920, Biblioteca del Congreso Nacional (opens in a new tab). More in Chile’s EPR law and batteries.

The four routes of a battery

Second life is route C of a scheme we apply the same way on all our service pages, so the same module always gets the same decision:

How do you hire the service?

1. InventoryYou tell us the chemistry, format, number of modules, year of commissioning and location.
2. Sample testWe measure a representative sample of the batch and estimate how many modules will fall into each route.
3. ProposalYou receive the result by route, with the destination of each group, the document that applies to each one and the quote.
4. Pickup and full testWe coordinate pickup with licensed hazardous-waste carriers and test the full batch in the laboratory.
5. DeliveryMatched blocks with their records, and a valorization certificate from the authorized receiving facility for what goes to recycling.

Price and lead times are confirmed in the quote. Pickup is organized as explained in battery and solar panel collection and transport. If the batch includes complete storage racks or containers, it is best to start with BESS end of life, where testing happens on site before anything is moved.

Frequently asked questions

Is any used battery suitable for second life?

No. Only modules with no mechanical damage, no thermal event and a measured state of health between 65% and 80% qualify. Above 80% it is better to repair or refurbish them and return them to their original use; below 65% the usable energy no longer covers the cost of integration and the module goes to recycling.

What is the difference between second life and refurbishment?

Refurbishment returns the battery to the same use: every cell is tested, the weak ones are replaced and the output capacity is measured. Second life moves the modules to a different function, almost always stationary storage, when they no longer perform in the original one but keep between 65% and 80% of their state of health.

How long does a second-life battery last?

It depends on the starting point and on the duty cycle. That is why we deliver the usable energy measured at handover, the internal resistance curve and a retest plan, instead of a promise in years. The warranty is set in the contract, by available energy and by period, not by time alone.

Can modules from different vehicles or manufacturers be mixed?

Not within the same block. We match by chemistry, format, capacity, internal resistance and cycle count, and keep blocks of different origin separate. A system can combine several blocks, each homogeneous and with its own management.

Can a system with second-life batteries be connected to the grid in Chile?

Chile’s electricity regulator (SEC) requires the lithium-ion batteries of a storage system and their BMS to meet IEC 62619, UL 1973 or UL 9540, and its technical instruction RGR No. 06/2024 does not mention used batteries. Check with the SEC and your licensed electrical installer before designing the project: declaring the installation is the owner’s responsibility.

Does second life count toward Chile’s EPR law?

The draft battery decree from Chile’s Ministry of the Environment proposes that at least 30% of the lithium-ion target be met through preparation for reuse. It is a text under consultation, not a rule in force: the ministry’s deadline to propose the decree is January 29, 2027.

Who is responsible if the system fails?

EcoBaterías is responsible for the modules it delivers, for their testing and for their usable-energy label. The electrical installation, its declaration and its operation are the responsibility of the project owner or their installer.

What happens to the modules that do not qualify?

They go to recycling. We manage its valorization with authorized receiving facilities, in Chile or in OECD countries where applicable; the authorized receiving facility closes the SIDREP declaration and issues the valorization certificate.

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