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Over-discharge protection

Verifies the battery system's over-discharge protection terminates discharging before damaging undervoltage occurs — exercised from a low starting SOC under stable discharge.
Clause (method) 8.2.15
Clause (pass criteria) 5.2.15
Object system
Status vs. 2020 revised (requirements)
Observation period 1 h at test environment temperature

Pass criteria

After the over-discharge protection test, the battery system shall show no leakage, no housing crack, no fire, and no explosion. The insulation resistance after testing shall not be less than 100 Ω/V (DC), or 500 Ω/V if an AC circuit is present.

Source: GB 38031-2025, clause 5.2.15 (PDF p. 12).

Pre-conditions

  • Object: The test object is a battery system. (8.2.15.1)
  • Ambient temperature: 20 °C ± 10 °C (or higher if specified by manufacturer). (8.2.15.2 a)
  • SOC: Adjust to a lower level within the normal operating range as recommended by the manufacturer (precise adjustment not required as long as the system can operate normally). (8.2.15.2 b)
  • Protection devices: All protection devices that affect functionality and are related to the test results shall be in normal operation. (8.2.15.2 c)
  • Contactors: All relevant main discharging contactors shall be closed. (8.2.15.2 c)
  • Insulation baseline: Measure before the test per Appendix B (clause 6.1.5).

Test parameters

Parameter Value Source
Ambient temperature 20 °C ± 10 °C (or higher per manufacturer) 8.2.15.2 a)
SOC at start Lower level within normal operating range 8.2.15.2 b)
Discharging equipment External, connected to main terminals 8.2.15.3 a)
Discharge current Stable current within the specified normal operating range, in consultation with the manufacturer 8.2.15.3 b)
Termination — auto cutoff Test object automatically terminates the discharging current 8.2.15.4 a)
Termination — signal Test object sends a signal to terminate the discharging current 8.2.15.4 b)
Termination — voltage floor If neither (a) nor (b), discharge until test object reaches 25 % of rated voltage 8.2.15.4 c)
Termination — temperature stable T stable (ΔT < 4 °C over 2 h) 8.2.15.4 d)
Post-test observation 1 h at test environment temperature 8.2.15.5

Procedure

  1. Confirm pre-treatment per 7.2 and measure baseline insulation per Appendix B. (6.1.5)
  2. Adjust SOC to a lower level within the normal operating range. (8.2.15.2 b)
  3. Bring ambient to 20 °C ± 10 °C (or higher per manufacturer). (8.2.15.2 a)
  4. Confirm all relevant protection devices are in normal operation and main discharging contactors are closed. (8.2.15.2 c)
  5. Connect the external discharging equipment to the main terminals. (8.2.15.3 a)
  6. In consultation with the manufacturer, set a stable discharge current within the specified normal operating range, and begin discharging. (8.2.15.3 b)
  7. Continue until any of: a. Test object automatically terminates the discharging current. (8.2.15.4 a) b. Test object sends a signal to terminate the discharging current. (8.2.15.4 b) c. If neither (a) nor (b), continue until the test object reaches 25 % of its rated voltage. (8.2.15.4 c) d. Test-object temperature stabilizes (ΔT < 4 °C over 2 h). (8.2.15.4 d)
  8. Disconnect external discharging and observe at the test environment temperature for 1 hour. (8.2.15.5)
  9. Re-measure insulation per Appendix B; inspect for leakage, housing cracks; confirm no fire/explosion.

After-test observation

Observe the test object for 1 hour at the test environment temperature (22 °C ± 5 °C) after discharging is terminated. (8.2.15.5)

What changed from GB 38031-2020

  • Listed in the preface change list as requirements revised (5.2.15). The test method (8.2.15) is not flagged in the preface as revised.

Migration impact: Already-type-approved vehicle models must comply from 2027-08-01. New type approvals from 2026-07-01. See Re-certification timeline.

Engineering notes (non-normative)

The notes below are practical interpretation, not part of the standard.

Engineering note (non-normative): The 25 %-of-rated-voltage floor (option c) is the deep-discharge endpoint when protection fails to act. For a typical Li-ion pack with ~3.7 V/cell nominal, that's roughly 0.9 V/cell — far below safe-storage minimums and well into copper-dissolution territory. Reaching this endpoint is a clear protection failure, but the cells must still survive without leakage/crack/fire/explosion to pass the test.

Engineering note (non-normative): Note that 5.2.15 is a requirements-only revision per the preface. Compared to 2020, the procedure is unchanged but the post-test pass bar (insulation, no leakage, etc.) was tightened or clarified. Cross-check the 2020 text for the exact delta when migrating an existing type-approved system.