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Immersion

Verifies the battery pack or system retains electrical safety after submersion — covering both saltwater contact (e.g., flood) and depth-rated freshwater ingress (IPX7). Choice of two methods with distinct pass criteria.
Clause (method) 8.2.6
Clause (pass criteria) 5.2.6
Object pack / system
Status vs. 2020 revised
Observation period 2 h at test environment temperature

Pass criteria

The pass criteria depend on which method is chosen (5.2.6):

Method 1 (3.5 % NaCl, 2 h): The test object shall show no fire or explosion. Leakage, housing cracks, and insulation degradation are not assessed for Method 1.

Method 2 (IPX7, 30 min, fresh water): The test shall meet the IPX7 requirements in GB/T 4208-2017, and the test object 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 5.2.6 (PDF p. 12).

Pre-conditions

  • Sequence: The test object must have already passed the 8.2.1 vibration test before immersion. (8.2.6.1)
  • Pre-treatment: Standard, per clause 7.2.
  • SOC: Highest working SOC per clause 6.1.10.
  • Connections: Wiring harness, connectors, and other components installed per the vehicle connection method. (8.2.6.2)
  • Insulation baseline: Measure before the test per Appendix B (clause 6.1.5).

Test parameters

Method 1 — sodium-chloride immersion

Parameter Value Source
Solution 3.5 % NaCl by mass in water 8.2.6.2 a)
Submersion Fully submerged in vehicle assembly orientation; water depth covers the test object 8.2.6.2 a)
Duration 2 h 8.2.6.2 a)

Method 2 — IPX7 fresh-water immersion

Parameter Value Source
Method base Per GB/T 4208-2017 §14.2.7 8.2.6.2 b)
Water Fresh water 8.2.6.2 b)
Orientation Manufacturer-specified installation state 8.2.6.2 b)
Submersion (object height < 850 mm) Lowest point ≥ 1 000 mm below water surface 8.2.6.2 b)
Submersion (object height ≥ 850 mm) Highest point ≥ 150 mm below water surface 8.2.6.2 b)
Duration 30 min 8.2.6.2 b)
Temperature constraint ΔT between water and test object ≤ 5 °C 8.2.6.2 b)

Procedure

  1. Confirm the test object has completed and passed the 8.2.1 vibration test. (8.2.6.1)
  2. Confirm pre-treatment per 7.2; measure baseline insulation per Appendix B. (6.1.5)
  3. Adjust SOC to highest working value. (6.1.10)
  4. Connect wiring harness, connectors, and other components per the vehicle connection method. (8.2.6.2)
  5. Choose Method 1 or Method 2.
  6. If Method 1: Place the test object in 3.5 % NaCl solution in vehicle assembly orientation. Ensure the water depth fully submerges it. Hold for 2 hours. (8.2.6.2 a)
  7. If Method 2: Verify ΔT(water ↔ object) ≤ 5 °C. Submerge in fresh water in manufacturer-specified installation orientation, with depth per height-based rule above. Hold for 30 min. (8.2.6.2 b)
  8. Remove the test object completely from the water.
  9. Let it stand at the test environment temperature for 2 hours. (8.2.6.3)
  10. Apply the relevant pass criteria (Method 1 vs. Method 2) per 5.2.6.

After-test observation

After removal from water, let the test object stand at the test environment temperature (22 °C ± 5 °C) for 2 hours. (8.2.6.3)

What changed from GB 38031-2020

  • Listed in the preface change list as requirements revised (5.2.6); test-method clause not flagged as revised.
  • The two-method structure with distinct pass criteria (no fire/no explosion vs. full STD + IPX7) is the headline requirements change.

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): Method choice has consequences. Method 1 (saltwater) imposes a softer pass bar (no fire/explosion) but tests the worst real-world ingress chemistry — chloride-driven corrosion of seals and pin housings. Method 2 (IPX7) is the harder pass bar but uses fresh water at controlled ΔT. A pack that passes Method 2 has not been demonstrated to survive Method 1, and vice versa. Pick the method that matches your most likely failure mode and document the rationale.

Engineering note (non-normative): The 8.2.6.1 sequencing — vibration must be passed first — exists because vibration is the realistic seal-integrity stressor. Immersing a fresh, unstressed pack overstates the field IP rating. Plan the test campaign so a single article sees vibration → immersion as a chain.

Engineering note (non-normative): The height-based submersion rule (850 mm threshold) handles tall packs that cannot fit 1 000 mm of head water in a typical lab tank. For tall systems the rule degrades to "150 mm above the highest point" — verify your tank can accommodate this before scheduling.