Low-Temperature Storage Testing for New Energy Vehicles

Low-temperature storage testing is an essential environmental reliability evaluation for new energy vehicles (NEVs), verifying that batteries, power electronics, and vehicle components can withstand prolonged exposure to extreme cold without degradation or safety failure. Conducted in accordance with international and national standards such as ISO 16750, IEC 60068-2-1, GB/T 2423.1, and GB 38031, this testing supports design validation, type approval, and market access for electric vehicles in cold-climate regions. This article explains the sample types, test items, methods, and applications of low-temperature storage testing for NEVs.

Technical Overview

New energy vehicles (NEVs), including battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and fuel cell electric vehicles (FCEVs), are frequently exposed to sub-zero ambient temperatures during winter parking, overnight storage, long-distance transport, and distribution to cold-climate markets. Low-temperature storage testing is a laboratory-based environmental test that subjects a vehicle, subsystem, or component to a defined low temperature for a specified duration while the sample is typically in an unpowered state, simulating real-world cold storage conditions.

The purpose of the test is to determine whether prolonged cold exposure causes irreversible changes in materials, sealing systems, electrical insulation, electrochemical performance, or mechanical integrity. Test severities typically range from -20°C to -40°C, with -40°C being the most widely specified extreme condition. Exposure durations commonly vary from 24 hours for component-level tests to extended periods for system-level and lifetime assessments.

The test is generally performed in accordance with recognized standards published by ISO, IEC, GB, UL, and other standards organizations, including:

• ISO 16750-4, which specifies climatic storage and operating tests for electrical and electronic equipment in road vehicles
• IEC 60068-2-1 (Test Aa/Ab), the fundamental cold test method for environmental testing of specimens
• GB/T 2423.1, the Chinese national environmental testing standard for cold tests, technically aligned with IEC 60068-2-1
• GB/T 28046.4, the Chinese adoption of ISO 16750-4 for automotive electrical equipment
• GB 38031 and GB/T 31467 series, covering safety requirements and test procedures for traction batteries of electric vehicles
• UL 2580 and IEC 62660 series, addressing battery safety and performance evaluation
• UN 38.3 (Test T.2, thermal test), relevant to transport of lithium cells and battery packs

Testing Samples

Complete Vehicles

Full-vehicle environmental exposure is conducted in large-scale climatic chambers or environmental proving grounds. Whole vehicles are cold-soaked to evaluate cold-start capability, door and lock mechanisms, glazing integrity, fluid behavior, high-voltage system readiness, and cabin system recovery after storage at temperatures as low as -40°C.

Power Battery Packs and Systems

Traction battery packs and battery systems are among the most temperature-sensitive assemblies in an NEV. Storage tests verify that the enclosure, cell-to-cell interconnections, insulation barriers, and battery management system (BMS) electronics survive cold exposure without cracking, delamination, insulation breakdown, or capacity loss.

Cells and Modules

At the cell and module level, low-temperature storage evaluates electrochemical stability, case and terminal integrity, and post-storage capacity recovery. These tests support cell qualification, supplier audits, and incoming quality control within the battery supply chain.

Power Electronics and Electronic Control Units

Motor controllers (inverters), onboard chargers (OBC), DC-DC converters, BMS controllers, vehicle control units (VCUs), sensors, and display modules are tested to ISO 16750-4 and GB/T 28046.4 severities to confirm solder joint integrity, component derating behavior, and enclosure robustness after cold storage.

Charging System Components

Charging inlets, couplers, high-voltage cables, and connectors are exposed to low temperature and subsequently evaluated for mating force, contact resistance, insulation resistance, and mechanical damage to housings and cable insulation, which become brittle at extreme cold.

Polymeric and Structural Materials

Plastic housings, gaskets, seals, adhesives, thermal insulation materials, and labeling are tested for brittleness, dimensional stability, and cracking after cold exposure, supporting material selection and part qualification.

Testing Items

Depending on the standard, product level, and customer specification, low-temperature storage testing typically includes the following evaluation items:

• Appearance inspection for cracking, deformation, delamination, leakage, corrosion, or discoloration after exposure and recovery
• Dimensional measurement to assess contraction-induced distortion or warpage
• Open-circuit voltage, internal resistance, and self-discharge measurements for cells and packs
• Capacity and capacity-recovery testing following storage and temperature stabilization
• Low-temperature discharge capability verification where required by the applicable specification
• Insulation resistance measurement of high-voltage circuits against accessible conductive parts
• Dielectric withstand (voltage withstand) testing to confirm electrical clearance and creepage integrity
• Continuity and contact-resistance checks on connectors, busbars, and harnesses
• Mating and unmating force testing of connectors after cold exposure
• Sealing integrity (IP code) verification to detect seal hardening or gasket shrinkage
• Functional and diagnostic checks of electronic control units after recovery

Testing Methods

Sample Preparation and Pre-Test Conditioning

Samples are inspected and documented before testing, including photographic records, dimensional data, and baseline electrical measurements such as state of charge, open-circuit voltage, and insulation resistance. Specimens are stabilized under standard atmospheric conditions (typically 23°C ± 5°C) in accordance with the conditioning requirements of IEC 60068-1 and the applicable product standard.

Cold Exposure Procedure

The sample is placed inside a climatic chamber conforming to the performance requirements of IEC 60068-3-5, with temperature uniformity and control accuracy adequate for the specified severity. The chamber temperature is reduced to the specified test temperature, commonly -40°C for storage applications, and held constant for the specified duration, typically no less than 24 hours for component storage tests and longer where system-level or extended storage evaluation is required. The specimen remains unpowered unless the specification requires an operational test, in which case IEC 60068-2-1 Test Ab applies. The sample temperature, rather than the chamber air temperature, governs the timing of the dwell period.

Recovery and Post-Test Evaluation

After the cold exposure period, the specimen is removed and allowed to recover under standard atmospheric conditions, with moisture droplets removed before electrical measurement to prevent invalid results. Final measurements and functional evaluations are then performed in the same sequence and under the same conditions as the baseline measurements, allowing direct comparison of pre-test and post-test data. Acceptance criteria are defined by the applicable standard or the customer specification, for example maintaining adequate insulation resistance and showing no visible damage or hazardous failure after storage.

Applications

Low-temperature storage testing serves multiple purposes across the NEV development and certification lifecycle:

• Design validation and product validation (DVPV) during vehicle and component development programs
• Regulatory compliance demonstration for traction battery safety under GB 38031 and related national requirements in China
• Type approval and homologation support for export to cold-climate markets in North America, Northern Europe, Russia, and other regions
• Transport safety assessment of lithium cells and battery packs under UN 38.3
• Supplier qualification, incoming inspection, and production quality surveillance for battery cells, modules, and electronic assemblies
• Durability and calendar-life studies, including assessment of long-term degradation after repeated thermal cycling and storage
• Root-cause analysis and failure reproduction for field returns originating from winter-season markets
• Support for cold-region field trials by providing laboratory evidence of storage robustness before proving-ground exposure

Accredited third-party laboratories commonly perform these tests under ISO/IEC 17025 management systems, issuing test reports that are recognized by regulators, OEMs, and certification bodies worldwide.

FAQ

What temperature is used for low-temperature storage testing of new energy vehicles?

The most common storage severity is -40°C, which represents the coldest automotive storage environment. Milder severities such as -30°C, -25°C, or -20°C may be specified depending on the target market, installation location, and applicable standard. ISO 16750-4 and GB/T 28046.4 assign different severity codes according to equipment mounting location and intended climatic region.

How long does the storage exposure last?

Typical component-level storage durations are 24 hours or more after the specimen reaches temperature stabilization. Battery and system-level programs may extend exposure over several days, and research-oriented calendar-aging studies can run for weeks or months. The exact duration is defined by the governing standard or customer technical specification.

What is the difference between low-temperature storage testing and low-temperature operation testing?

Storage testing is performed while the specimen is unpowered, evaluating survival of cold exposure without electrical function. Operation testing, by contrast, requires the specimen to be powered and functional at the low temperature, assessing performance parameters such as discharge capacity, power output, and control accuracy under cold conditions. Storage testing is normally completed first, followed by recovery and then operational evaluation if required.

Is the sample powered or discharged during the test?

For storage tests the sample is generally de-energized and held at a specified state of charge, often a mid-range level defined by the test plan. Energized testing is a separate procedure governed by different standard clauses and safety considerations.

What criteria determine whether the sample passes the test?

Acceptance criteria typically include no visible damage such as cracking or leakage, no hazardous events such as fire or explosion for battery samples, insulation resistance above the specified minimum, no dielectric breakdown, and preservation of functional performance within defined tolerances after recovery. Specific limits are established by the applicable standard, such as the traction battery safety requirements of GB 38031, or by contractual specification.

Which standards are most relevant for battery pack storage evaluation in China?

The GB/T 31467 series, GB/T 31484 and GB/T 31485 series, and GB 38031 define the principal requirements and test procedures for traction batteries of electric vehicles in China, while environmental test methods reference GB/T 2423.1 and GB/T 28046.4. International programs frequently reference ISO 12405, IEC 62660, UL 2580, and UN 38.3.

Why is low-temperature storage testing important for NEVs?

Cold storage can embrittle polymers, reduce electrolyte conductivity, harden seals, degrade adhesives, and stress solder joints, any of which may lead to failure when the vehicle is restarted or recharged. Systematic laboratory evaluation identifies these risks before mass production, protects user safety, and ensures warranty performance in winter climates.