Over-Discharge Repair Experiment: Can Lithium Cobalt Oxide Batteries Below 2.5V Be Saved?
Over-discharged lithium cobalt oxide (LiCoO₂) batteries below 2.5V per cell are often deemed dead, but some can still be salvaged with caution. Lab tests show a 50-60% recovery success rate if cells aren’t physically damaged. This guide explains how to safely revive such batteries while minimizing fire risks and performance loss.
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1. Gradual Low-Current Charging
Step 1: Use a charger with a “recovery mode” or manually set the current to 0.05C (e.g., 0.25A for a 5000mAh battery).
Step 2: Monitor voltage rise. If it climbs to 3.0V within 1 hour, continue charging at 0.1C. If stuck below 2.7V for 2 hours, discard the battery.
2. Post-Recovery Capacity Test
Fully charge the battery, then discharge it at 0.5C. Measure actual capacity:
Recoverable: ≥80% original capacity.
Degraded: 50-79% capacity—use only for low-power tasks.
Unsafe: <50% or voltage drops >0.5V under load.
3. Critical Warning Signs
Swelling or Leaks: Immediate disposal required.
High Internal Resistance: >150mΩ per cell (test with a multimeter).
Self-Discharge Rate: Losing >0.1V/day after recovery.
Why Recovery Is Risky
LiCoO₂ cells discharged below 2.5V suffer copper dissolution, creating internal shorts. For example, a “recovered” 4S battery might work briefly but suddenly fail mid-flight, crashing your drone.
Success Rate Data
Lab Tests: 55% of mildly over-discharged cells (2.3V–2.5V) regained 85% capacity. Field Tests: Only 30% of heavily drained cells (1.8V–2.2V) stabilized after recovery.
When to Give Up
Voltage <2.0V: Recovery success drops below 10%.
Multiple Over-Discharges: Batteries cycled below 2.5V twice rarely hold charge.
Conclusion
While lithium cobalt oxide batteries below 2.5V can sometimes be revived, success depends on discharge depth and recovery methods. Use ultra-low currents for charging and rigorously test capacity post-repair. For critical missions, always replace questionable batteries—safety outweighs savings.
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