First, the state of the battery itself. For example, are there any problems in the production process, such as the quality of raw materials, manufacturing process, or battery aging. If it is a new battery, it may not be activated yet, and the active substances inside have not fully played their role, resulting in low initial discharge capacity.
1. The battery is not fully activated
- Cause: Some batteries (such as lithium-ion batteries and nickel-metal hydride batteries) require a complete charge and discharge cycle before the first use to activate the electrode material, fully infiltrate the electrolyte, and improve the utilization rate of the active material.
- Solution:
a. Perform 2-3 complete charge and discharge cycles (0.2C~0.5C rate) as recommended by the manufacturer.
b. Avoid using fast charge or high-rate discharge directly before the first discharge.
2. Influence of test environment temperature
- Cause: Low temperature (such as below 10℃) will significantly reduce the ion migration rate of the battery, resulting in a decrease in available capacity; high temperature (such as above 40℃) may accelerate side reactions and reduce effective energy.
- Solution:
a. Test at standard temperature (25℃±2℃).
b. If low temperature/high temperature testing is required, refer to the temperature compensation parameters in the battery specification.
3. Initial battery state of charge (SOC) calibration error
- Cause:
a. New batteries may not be fully charged when leaving the factory (e.g., storage SOC is 30%~50%).
b. The SOC estimation of the battery management system (BMS) is inaccurate when used for the first time.
- Solution:
a. Fully charge before testing (constant current and constant voltage charging to the cutoff current).
b. Calibrate the BMS SOC algorithm through multiple cycles.
4. Self-discharge causes power loss
- Cause:
a. The battery loses power due to self-discharge after long-term storage (the self-discharge rate of lithium-ion batteries is about 2%~5%/month).
b. Micro short circuits or impurities inside the battery cause abnormal self-discharge.
- Solution:
a. Charge first and then test after long-term storage.
b. Check the battery voltage consistency and eliminate abnormal self-discharging cells.
5. Improper test parameter settings
- Discharge rate is too high:
High rate (such as 1C or above) discharge will cause the available capacity to be lower than the nominal value due to polarization effect.
- Wrong cut-off voltage setting:
If the cut-off voltage is too high (e.g., set the lithium-ion battery to 3.0V instead of 2.5V), the discharge will be terminated prematurely.
- Solution:
a. Select the standard discharge rate (e.g., 0.2C) according to the battery specification.
b. Check whether the cut-off voltage is consistent with the battery chemistry system (e.g., ternary lithium batteries are usually 2.8V~3.0V).
6. Battery manufacturing defects or aging
- Cause:
a. Manufacturing defects such as uneven electrode coating and insufficient electrolyte.
b. Long storage time leads to SEI film thickening (lithium-ion batteries) or active material passivation.
- Solution:
a. Compare the capacity of batteries in the same batch to check whether it is a single cell problem.
b. Aging batteries can try to restore some capacity by charging and discharging with low current.
7. Protection mechanism triggered
- Cause:
The BMS triggers protection due to abnormal voltage/temperature/current, terminating the discharge prematurely.
- Solution:
a. Check the BMS log to confirm whether over-discharge, overcurrent or temperature protection is triggered.
b. Adjust the test conditions to match the BMS protection threshold.
Recommended troubleshooting steps
- Check the initial SOC: Make sure the battery is fully charged before testing (the voltage reaches the upper limit, such as 4.2V for ternary lithium batteries).
- Calibrate the test equipment: Verify the accuracy of the voltmeter and current sensor.
- Control the ambient temperature: Make sure the test is performed in a 25℃ constant temperature box.
- Optimize the test parameters: Use a low rate (0.2C~0.5C) and the correct cutoff voltage.
- Repeat the test: Observe whether the capacity recovers after 2-3 cycles.
If the problem persists, it is recommended to contact the battery supplier to provide a factory capacity test report, or perform a disassembly analysis (such as X-ray detection of electrode structure, electrolyte composition analysis, etc.).
