Testing and Evaluation of New Energy Batteries for Echelon Utilization (Second-Life Applications)

Echelon utilization testing provides a scientific basis for repurposing retired electric vehicle batteries into safe and reliable second-life applications. Accredited third-party laboratories evaluate residual capacity, internal resistance, self-discharge behavior, safety performance, and consistency in accordance with recognized standards such as the GB/T 34015 series, UL 1974, IEC 62619, and IEC 63330. This article outlines the technical framework, testing items, methods, and application scenarios for new energy battery echelon utilization testing and evaluation.

Technical Overview

Echelon utilization, also known as cascade utilization or second-life application, refers to the practice of repowering lithium-ion traction batteries that have been retired from electric vehicles. When an EV battery degrades to approximately 70 to 80 percent of its original rated capacity, it can no longer meet the range and power demands of vehicle traction, yet it still retains substantial usable energy. By screening, grading, re-grouping, and re-certifying these retired batteries, they can be deployed in less demanding stationary or low-power applications, extending their service life by five to eight years before final material recycling.

Because retired batteries carry uncertainties in degradation history, cell-to-cell consistency, and latent internal defects, professional testing is the critical gateway to safe echelon utilization. Unqualified screening can introduce serious risks, including capacity mismatch, accelerated self-discharge, internal short circuits, thermal runaway, and fire hazards in the field. A structured testing and evaluation program therefore serves three purposes: quantifying the true residual value of retired batteries, eliminating unsafe units from the repurposing stream, and verifying that reassembled echelon products satisfy the safety and reliability requirements of their target applications.

The technical framework for echelon utilization testing draws on several standards families. In China, the GB/T 34015 series specifies residual capacity testing, product requirements, and dismantling procedures for echelon utilization of traction batteries, while GB/T 33598 addresses dismantling requirements and GB 38031 defines traction battery safety requirements. Internationally, UL 1974 describes the evaluation of batteries for repurposing, IEC 63330 establishes requirements for repurposing secondary lithium batteries, IEC 62619 covers safety of secondary lithium cells for industrial applications, and IEC 62660 addresses cell-level testing for electric vehicle propulsion. UN 38.3 applies when repurposed products must be transported. Accredited third-party laboratories conduct evaluations against these frameworks to deliver traceable, defensible test reports.

Typical objectives of an echelon utilization evaluation include:

• Determination of residual capacity, residual energy, and state of health (SOH)
• Assessment of internal resistance, power capability, and efficiency
• Screening of abnormal self-discharge and latent micro-short-circuit cells
• Verification of safety performance under abuse and environmental conditions
• Consistency grading and matching of cells or modules for re-grouping
• Prediction of remaining useful life (RUL) for the intended second-life application

Testing Samples

Retired Battery Cells

Individual cylindrical, prismatic, or pouch cells recovered from retired EV packs are the most fundamental test units. Cell-level evaluation focuses on residual capacity, internal resistance, self-discharge rate, and safety margins, because cell consistency ultimately determines the performance ceiling of any reassembled echelon product. Cells are typically tested after deep-discharge pretreatment and removal from module structures.

Retired Battery Modules

Modules, comprising multiple cells with original busbars, sensors, and mechanical frames, are the most common unit for echelon repurposing because disassembly to the cell level is costly and increases damage risk. Module testing verifies residual capacity, voltage consistency across cell groups, insulation performance, and structural integrity, and confirms that the module can be directly integrated into echelon products such as energy storage cabinets.

Retired Battery Packs

Complete retired packs are evaluated for overall residual energy, BMS functionality, communication protocols, high-voltage insulation, and pack-level safety. Pack evaluation helps determine whether a pack can be reused as an integral unit or must be dismantled to the module level. Historical operating data extracted from the BMS, including mileage-equivalent cycles, deep-discharge events, and fault records, supplements laboratory measurement.

Reassembled Echelon-Utilization Products

Newly re-grouped battery systems built from graded retired cells or modules, such as echelon energy storage battery cabinets, base station backup power units, or low-speed vehicle packs, must undergo complete type testing before market entry. This includes electrical performance, safety abuse, environmental adaptability, and functional verification of the newly configured BMS and protection circuits.

Testing Items

Testing programs are tiered from rapid incoming screening to full type evaluation. Core test categories and representative items are summarized below.

Basic Characterization and Pretreatment Inspection

• Appearance inspection: deformation, leakage, corrosion, cracks, and terminal damage
• Dimension and weight measurement for sorting and binning
• Open-circuit voltage (OCV) measurement and voltage consistency screening
• Insulation resistance and withstand voltage testing of high-voltage assemblies
• Verification of nameplate information against BMS historical data and traceability records

Electrical Performance Testing

• Residual capacity and residual energy measurement at specified rates and temperatures
• State of health (SOH) calculation relative to rated capacity
• AC internal resistance and DC internal resistance testing
• Rate capability testing at different charge and discharge multiples
• Energy efficiency and round-trip efficiency measurement
• Self-discharge rate determination through standing voltage-decay monitoring
• Charge retention and capacity recovery testing
• Voltage, capacity, and internal resistance consistency grading for grouping decisions

Safety Performance Testing

• Overcharge and forced over-discharge testing
• External short circuit testing
• Thermal abuse and heating testing
• Temperature cycling and thermal shock testing
• Mechanical integrity: vibration, shock, and crush testing
• Insulation fault, reverse connection, and protection function verification
• Thermal runaway propagation assessment for module and pack configurations

Environmental Adaptability Testing

• Low-temperature and high-temperature discharge performance
• Damp heat and humidity cycling resistance
• Salt spray corrosion resistance for outdoor stationary installations
• IP rating verification (dust and water ingress protection) for enclosure-level products

Lifespan and Reliability Evaluation

• Cycle life testing under application-relevant charge and discharge profiles
• Calendar aging assessment at elevated storage temperatures
• Remaining useful life (RUL) prediction based on degradation modeling

Testing Methods

Testing methodologies combine standard-condition laboratory procedures with data-driven diagnostic techniques to balance accuracy, throughput, and cost.

Residual Capacity Measurement

Residual capacity is measured through a controlled full charge followed by constant-current discharge to the specified cut-off voltage under a reference temperature, in accordance with the GB/T 34015 series and UL 1974. Multi-rate discharge testing is applied when the target application involves discharge profiles that differ from vehicle traction loads. The measured capacity, combined with original rated capacity, yields the SOH value used for grading decisions.

Internal Resistance and Power Characterization

AC internal resistance at 1 kHz provides a fast screening indicator, while DC internal resistance is characterized using hybrid pulse power characterization (HPPC) profiles that apply defined charge and discharge current pulses and record the transient voltage response. Pulse test results are used to evaluate whether retired cells and modules retain sufficient power capability for the intended stationary or mobility application.

Self-Discharge Screening

Elevated self-discharge indicates internal micro-short circuits, a leading cause of field failures in echelon products. Samples are charged to a defined state of charge and monitored over standing periods, with voltage decay curves compared against statistical thresholds. High-voltage storage combined with extended OCV tracking enables rapid identification of abnormal units before they enter re-grouping.

Non-Destructive Inspection

X-ray and computed tomography (CT) imaging detect electrode deformation, lithium plating, welding defects, and internal contamination without destroying the sample. Infrared thermography during charging and discharging reveals localized hot spots caused by high-resistance connections or defective cells. These methods supplement electrical screening and improve confidence in module-level reuse decisions.

Safety Abuse Testing

Safety evaluation follows the abuse test matrices of GB 38031, UL 1974, and IEC 62619, including overcharge, over-discharge, external short circuit, thermal abuse, crush, vibration, and temperature cycling. Tests are conducted in purpose-built chambers with blast protection, gas analysis, and calorimetric monitoring. For echelon products deployed in residential or communication infrastructure settings, thermal runaway propagation behavior is given particular attention.

Data-Driven State Estimation

Historical BMS data, including accumulated throughput, temperature exposure, and abuse events, is fused with laboratory measurement results through SOH estimation and degradation modeling algorithms. Electrochemical impedance spectroscopy (EIS) can further separate aging mechanisms such as loss of active material and loss of lithium inventory. This combined approach improves the accuracy of remaining useful life prediction and supports warranty definition for echelon products.

Applications

Tested and graded retired batteries serve a broad range of second-life applications where energy density and power demands are moderate and cost sensitivity is high. Major application scenarios include:

• Grid-side and distributed energy storage, including peak shaving, valley filling, and renewable energy smoothing for solar and wind installations
• Backup power for telecommunication base stations and data centers, replacing lead-acid batteries with higher cycle life
• Commercial and residential energy storage systems integrated with photovoltaic generation and emergency power supply functions
• Low-speed electric vehicles such as electric bicycles, tricycles, golf carts, forklifts, and sightseeing vehicles
• Off-grid power for street lighting, traffic monitoring, and agricultural equipment in rural electrification projects
• Uninterruptible power supply (UPS) systems for industrial facilities, hospitals, and communication hubs
• Portable and mobile energy storage for construction sites, emergency rescue, and outdoor events

Each application imposes distinct duty profiles, ambient conditions, and safety expectations, so testing parameters such as rate, temperature range, and cycle profiles are tailored to the intended deployment scenario during evaluation program design.

FAQ

What is echelon utilization of new energy batteries?

Echelon utilization is the graded reuse of traction batteries retired from electric vehicles. After vehicle service, batteries typically retain 70 to 80 percent of their rated capacity, which remains sufficient for less demanding applications such as stationary energy storage, backup power, and low-speed vehicles. Testing ensures these batteries are safely and economically redeployed before final recycling.

What residual capacity qualifies a retired battery for echelon utilization?

Industry practice generally considers batteries with residual capacity between 70 and 80 percent of rated capacity as candidates for echelon utilization. Units below this threshold are usually routed directly to material recycling. Final decisions also depend on internal resistance, self-discharge behavior, safety test results, and the requirements of the target application.

Which standards govern echelon utilization testing?

Primary references include the GB/T 34015 series for residual capacity testing and echelon product requirements, GB/T 33598 for dismantling, GB 38031 for traction battery safety, UL 1974 for battery repurposing evaluation, IEC 63330 for repurposing requirements, IEC 62619 for industrial battery safety, and IEC 62660 for cell-level evaluation. UN 38.3 applies to transport safety of repurposed products.

How long does a typical echelon utilization evaluation take?

Screening-level evaluation of residual capacity, internal resistance, and self-discharge typically requires one to two weeks per batch. Full type testing of reassembled echelon products, including safety abuse and environmental testing, generally requires four to eight weeks depending on sample count and test matrix complexity. Cycle life verification may require extended durations and is often performed with accelerated protocols combined with modeling.

What information should be provided when submitting samples?

Submitters should supply battery specifications, rated capacity and voltage, original vehicle application details, available BMS historical data, traceability coding, declared state of charge, and the intended echelon application. Samples should be discharged to a safe transport state of charge and packaged in accordance with dangerous goods transport regulations before delivery to an accredited third-party laboratory.

Can echelon products obtain third-party certification?

Yes. Reassembled echelon energy storage and backup power products can undergo type testing and certification against applicable GB, IEC, and UL standards through accredited third-party laboratories. Certification verifies that graded retired batteries, new BMS electronics, and enclosure designs jointly satisfy the safety, performance, and environmental requirements of the destination market.