Can old and new 18650 lithium batteries be mixed in a battery pack?
2024-07-23
It is usually not recommended to mix old and new 18650 lithium batteries in a battery pack.
The reasons are mainly concentrated in the following aspects:
1. Inconsistent capacity: The capacity of new batteries is usually greater than that of old batteries. The capacity difference will cause uneven performance of the battery pack during charging and discharging. The old battery may be discharged prematurely or fully charged first during charging, affecting the overall performance.
2. Different internal resistance: The internal resistance of old batteries is usually larger, which will cause uneven voltage distribution of each battery during charging and discharging, increase the risk of overcharging or over-discharging, and thus affect the life and safety of the battery pack.
3. Cycle life difference: The cycle life of new and old batteries is different. The old battery has experienced more charge and discharge cycles and its performance has declined. When mixed, the aging rate of new and old batteries is different, and the performance of the overall battery pack will be unstable.
4. Safety hazards: Mixing new and old batteries may cause voltage imbalance in the battery pack, increase the risk of thermal runaway of the battery pack, and have potential safety hazards, such as overheating, leakage, and even fire or explosion.
If you must mix batteries in special circumstances, you can consider the following measures:
1. Matching capacity: Choose batteries with smaller capacity differences to mix and use to reduce the impact of imbalance.
2. Balancing circuit: Use a battery management system (BMS) or balancing circuit to monitor and manage the status of each battery to ensure balanced charging and discharging.
3. Regular testing: Regularly check the performance of the battery pack and replace batteries with significantly reduced performance in a timely manner.
In short, in order to ensure the performance and safety of the battery pack, the best practice is to avoid mixing new and old 18650 lithium batteries.
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Can 18650 batteries with different capacities be connected in series or in parallel?
