For the 12V150Ah LiFePO4 batteries (shipped at 50% SOC) as agreed for land transportation, the customer wishes to confirm the SOC compliance by voltage measurement upon receipt.

Technical analysis: Due to the characteristic flat charge/discharge voltage plateau of LiFePO4 batteries, there is no linear correlation between SOC (State of Charge) and voltage. Therefore, the customer cannot accurately determine the actual battery SOC simply by measuring voltage.

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LiFePO4 batteries exhibit an extremely flat voltage plateau (3.2V~3.3V), making SOC estimation via voltage unreliable. Key data:

SOC Range	Open-Circuit Voltage (V)	Voltage Behavior	Detection Advice
Low SOC (0%~30%)	2.50~3.25	Voltage drops rapidly with SOC	Voltage method usable (±5% SOC)
Plateau (30%~70%)	3.25~3.31	Minimal voltage change (±0.06V)	Capacity test required
High SOC (70%~100%)	3.31~3.45	Voltage rises slowly with SOC	Voltage method辅助usable (±8% SOC)

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We ensure 50% SOC via precision capacity calibration:

• Step 1: Charge to 100% SOC or discharge to 0% SOC;
• Step 2: Adjust SOC by charging/discharging to target (e.g., discharge 50% to reach 50% SOC);
• Step 3: Measure voltage after 24h rest for consistency.

For balance of efficiency and accuracy:

• Voltage Screening (100% Test):
  • Criteria: Rested voltage ≥3.29V (excludes low-SOC cells);
  • Note: Batteries must rest ≥24h at 25±2℃.
• Capacity Spot Check (Mandatory):
  • Sampling: ≥10% (focus on plateau-region batteries);
  • Method: Discharge at 0.5C to 2.5V to calculate actual SOC.

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• Technical Limitation: 50% SOC falls in the "voltage dead zone" (3.25~3.31V).
• Risk: Voltage-only checks may misjudge SOC.