Power Battery Low-Temperature Discharge Testing: Procedures, Standards, and Evaluation Criteria

Power battery low-temperature discharge testing evaluates how much capacity, energy, and power an electric vehicle traction battery can deliver under sub-zero ambient conditions, making it one of the most critical performance verifications for cold-climate operation. Conducted in accordance with recognized standards such as GB/T 31486, IEC 62660, and ISO 12405, this test supports winter range validation, battery management system calibration, and product certification by accredited third-party laboratories.

Technical Overview

Low-temperature discharge testing is a laboratory evaluation that measures the ability of a power battery, the traction battery of an electric or hybrid vehicle, to release electrical energy when the cell, module, or pack is exposed to sub-zero ambient temperatures. The test quantifies capacity retention, deliverable energy, voltage behavior, and power capability under cold conditions, providing an objective basis for judging whether a battery can meet the real-world demands of winter driving in cold-climate regions.

The underlying physics makes this test essential. As temperature drops, the ionic conductivity of the electrolyte decreases while its viscosity increases, charge-transfer resistance at the electrode surfaces rises, and solid-state diffusion of lithium ions within electrode active materials slows dramatically. The observable consequences include pronounced voltage sag under load, reduced usable capacity, and significant power derating. Low-temperature charging carries additional risks such as lithium plating on the anode, but low-temperature discharge testing focuses on the output side: how much energy the battery can actually deliver when a driver needs it in winter conditions.

Applicable Standards

• GB/T 31486: Chinese national standard specifying electrical performance requirements and test methods for electric vehicle traction battery cells and modules, including the low-temperature discharge test at minus 20 degrees Celsius.
• IEC 62660-1: International standard covering performance testing of secondary lithium-ion cells for the propulsion of electric road vehicles, including discharge tests across a defined temperature range.
• ISO 12405 series: Standards for electric performance and endurance testing of lithium-ion battery packs and systems used in electrically propelled road vehicles.
• UL 2580: Standard for batteries for use in electric vehicles, which references environmental and performance characterization including low-temperature behavior.
• GB 38031: Safety requirements standard for traction batteries of electric vehicles, applied in conjunction with performance standards to confirm that no safety events occur during or after temperature stressing.

Testing Samples

Power Battery Cells

Individual lithium-ion cells, including cylindrical, prismatic, and pouch formats in chemistries such as nickel-manganese-cobalt, lithium iron phosphate, and nickel-cobalt-aluminum, constitute the most common test samples. Cell-level testing isolates the fundamental low-temperature capability of the electrochemical system from the influence of pack-level thermal design, and it is the level at which acceptance thresholds such as the GB/T 31486 capacity retention requirement are most frequently applied.

Battery Modules

Modules, which combine multiple cells with busbars, sensing harnesses, and structural framing, are tested to evaluate consistency across interconnected cells and to observe thermal gradients that emerge during cold discharge. Module testing bridges cell characterization and full-pack validation and is useful for identifying weak cells, connection losses, and uneven current distribution under cold conditions.

Battery Packs and Systems

Complete packs with integrated battery management systems, contactors, and cooling or heating circuits are tested at the system level under frameworks such as the ISO 12405 series. These tests can be executed with thermal management inactive, to characterize the bare battery, or with a defined preheating strategy active, to validate the effectiveness of the vehicle-level cold-start approach.

Testing Items

Depending on the sample level and the governing specification, a low-temperature discharge evaluation typically encompasses the following measured quantities:

• Low-temperature discharge capacity: the ampere-hour output delivered at the specified cold temperature and discharge rate, compared against the room-temperature reference capacity.
• Capacity retention ratio: the percentage expression of the cold-temperature capacity relative to the rated capacity or the room-temperature capacity.
• Low-temperature discharge energy: the watt-hour output integrated over the discharge, which more directly reflects usable winter driving range than ampere-hour capacity alone.
• Discharge voltage characteristics: open-circuit voltage before discharge, the shape and level of the voltage plateau, terminal voltage sag under load, and the point at which the cut-off voltage is reached.
• Rate and power capability: performance at elevated discharge currents at low temperature, characterizing how much acceleration and load power the battery can supply in cold conditions.
• DC internal resistance change: the increase in effective resistance at low temperature, which drives voltage sag and heat generation.
• Recovery capacity: the room-temperature capacity measured after the sample returns to ambient temperature and is fully recharged, distinguishing reversible cold-induced loss from permanent degradation.
• Safety observations: recording of any leakage, venting, case deformation, smoke, fire, or explosion during or after the test.

Testing Methods

Pre-Test Preparation and Reference Capacity

Samples are first inspected for mechanical damage, corrosion, and markings, and their insulation resistance is verified where required. The sample is then stabilized at room temperature, typically 25 degrees Celsius plus or minus 2 degrees, and charged using the standard charging method specified by the manufacturer, commonly constant-current followed by constant-voltage. A room-temperature discharge at the reference rate, often 1I1, is performed to termination voltage to establish the reference capacity. Where the standard requires verification, consecutive reference discharges should agree within the specified tolerance before proceeding.

Low-Temperature Conditioning

The fully charged sample is placed in a climatic chamber set to the target temperature, characteristically minus 20 degrees Celsius plus or minus 2 degrees for cell and module testing under GB/T 31486, with colder setpoints such as minus 30 or minus 40 degrees Celsius used for extreme-environment programs. The soak duration is typically at least 20 hours, or until thermocouples on the sample surface confirm thermal equilibrium with the chamber setpoint, ensuring the cell core has genuinely reached the test temperature rather than only its surface.

Discharge Execution

While the chamber maintains the target temperature, the sample is discharged at the specified constant current, for example 1I1 at minus 20 degrees Celsius in cell-level GB/T 31486 testing, until the termination voltage defined by the cell or system specification is reached. Throughout the discharge, current, voltage, and surface temperature are recorded continuously. The test captures total ampere-hour throughput, integrated energy, the complete voltage curve, temperature rise caused by internal heat generation, and the time required to reach the cut-off condition.

Recovery and Post-Test Inspection

After discharge, the sample rests in the chamber and is then returned to room temperature. It is recharged using the standard method and discharged again at room temperature to determine recovery capacity, which reveals whether the cold exposure caused any irreversible capacity loss. The sample undergoes a final visual and dimensional inspection, and any anomaly such as leakage or deformation is documented and treated as a test failure under most specifications.

Acceptance Criteria

Under GB/T 31486, the discharge capacity of cells at minus 20 degrees Celsius must commonly reach no less than 70 percent of rated capacity, with module-level and system-level thresholds defined by the applicable product standard or the manufacturer specification. Acceptance in all cases additionally requires the absence of fire, explosion, or leakage, and many programs impose requirements on recovery capacity at room temperature. Deviation from the voltage envelope or excessive internal resistance growth, even when capacity passes, is typically flagged for engineering review because it predicts poor power delivery in service.

Applications

Low-temperature discharge data feeds directly into nearly every stage of power battery development, validation, and market access:

• Winter range validation: quantifying the energy a vehicle can actually deliver in cold climates, supporting honest range claims and customer expectation management.
• Battery management system calibration: building state-of-charge estimation tables, state-of-power limits, and derating maps that depend on temperature-dependent discharge characteristics.
• Thermal management development: sizing and tuning preheating strategies, coolant circuits, and heating films by comparing cold discharge behavior with and without active warming.
• Cell screening and quality control: comparing batches of production cells for low-temperature consistency as part of incoming inspection and supplier qualification.
• Certification and market access: generating the test evidence required for type approval and homologation in cold-climate markets, executed by accredited third-party laboratories.
• Research and benchmarking: comparing electrolyte formulations, electrode materials, and cell designs during development of next-generation chemistry with improved cold performance.
• Energy storage deployment: qualifying stationary batteries for outdoor installations in northern regions where winter performance dictates usable capacity.

FAQ

What test temperature is typically used for low-temperature discharge testing?

Minus 20 degrees Celsius is the most common setpoint for cell and module testing under GB/T 31486 and appears in IEC 62660 performance profiles. Programs targeting extreme-cold markets, such as Nordic, North American, or high-altitude applications, frequently add setpoints of minus 30 or minus 40 degrees Celsius.

Why must the sample soak at temperature for 20 hours or more?

A long soak guarantees thermal equilibrium deep inside the cell core, not just at the surface. Because lithium-ion cell cores have significant thermal mass and relatively poor internal heat conduction, shorter soaks would test a partially warm battery and produce optimistic, non-repeatable results.

What is the typical pass criterion for the test?

The most widely applied requirement is that discharge capacity at minus 20 degrees Celsius reaches no less than 70 percent of rated capacity for cells, together with the absence of any safety event such as fire, explosion, or leakage. Exact thresholds for modules, packs, and specific products are defined by the governing standard or the purchase specification.

How does low-temperature discharge testing differ from low-temperature charging testing?

Discharge testing measures how much energy the battery can deliver when cold, whereas charging tests evaluate how safely and efficiently it can accept energy when cold. Charging at low temperature is generally more hazardous because lithium plating on the anode can occur, so the two evaluations use different currents, protections, and acceptance logic.

Can a battery pack with liquid heating be tested at low temperature?

Yes. System-level testing under the ISO 12405 framework can be run with thermal management disabled to characterize intrinsic capability, or with a defined preheating sequence enabled to validate the cold-start strategy. Both configurations deliver valuable but distinct engineering information.

What equipment is required to perform the test?

A temperature-controlled climatic chamber with adequate uniformity, a programmable battery test system capable of the required charge and discharge currents, multi-channel data acquisition for voltage and temperature, and appropriate safety provisions including fume extraction and fire suppression are the essential elements found in accredited third-party laboratories and well-equipped in-house facilities.