Hi all,
Can anyone advise here please.
I can understand that all recharge batteries degrade over time and loose there ability to charge and hold that charge.

Question is, what would cause these batteries to fluctuate?
Even with Li-Ion, For example, the battery could charge to 1500 mAh, next charge it could be down to 900mAh, then on the next charge it could be 1400mAh.

thanks in advance.

Even though the same charger is used, and the temperature around the battery and charger is always the same.

 

Battery fluctuations, even in high-quality lithium-ion (Li-ion) batteries, can be caused by several factors. Here are some potential reasons for the variations in charging capacity:

1. State of Charge (SOC) and Depth of Discharge (DOD):
   • SOC: The battery's charge level when it starts charging can influence the charging capacity. If the battery is not completely discharged before recharging, the charge cycle may be affected, leading to variations.
   • DOD: The extent to which the battery is discharged before recharging can impact its capacity. Deep discharges can stress the battery more than shallow discharges, leading to fluctuations.
2. Battery Age and Degradation:
   • Over time, the internal components of a battery degrade. This can cause inconsistent charging and discharging behaviors. The formation of solid electrolyte interphase (SEI) layers, loss of active materials, and other aging processes can lead to capacity fluctuations.
3. Charge and Discharge Rates:
   • Charging and discharging the battery at different rates can cause fluctuations. High current rates can lead to increased internal resistance and heat generation, impacting the battery's ability to hold a consistent charge.
4. Battery Management System (BMS):
   • The BMS is responsible for monitoring and managing the battery's performance. If the BMS has inconsistencies or errors, it can cause fluctuations in reported capacity. Calibration errors or software glitches in the BMS can lead to inaccurate readings.
5. Temperature Effects:
   • Even slight variations in temperature can affect the battery's performance. Although you mentioned the temperature is constant, micro-environmental changes or internal temperature variations during charging and discharging cycles can cause fluctuations.
6. Cell Balancing:
   • In multi-cell batteries, if the cells are not balanced properly, some cells may charge or discharge faster than others, leading to fluctuations in overall capacity.
7. Electrolyte and Chemical Composition:
   • Variations in the electrolyte composition and chemical reactions within the battery can lead to fluctuations. Impurities or inconsistencies in the manufacturing process can also contribute to this issue.
8. Measurement Accuracy:
   • The method and tools used to measure the battery capacity can also introduce errors. Inaccurate measurement devices or techniques can report fluctuating capacities.

To mitigate these fluctuations, consider the following practices:

• Regular Calibration: Periodically fully charge and fully discharge the battery to recalibrate the BMS.
• Moderate Use: Avoid deep discharges and overcharging. Keep the battery within a moderate SOC range (e.g., 20% to 80%).
• Optimal Charging Rates: Use chargers that provide a stable and appropriate current for the battery.
• Proper Storage: Store the battery at a moderate temperature and charge level when not in use for extended periods.

 

Thanks