Lithium batteries of different capacities can be connected in parallel, but they need to be operated carefully and meet certain conditions.

I. Theoretical feasibility

In principle, lithium batteries in parallel is feasible. Parallel connection can increase the total capacity while keeping the voltage constant. When lithium batteries of different capacities are connected in parallel, their terminal voltages should ideally be equal, so that after the parallel operation, the external output voltage of the entire battery pack is the same as that of a single battery.

2. Potential risks

Capacity variance problem

Lithium batteries with different capacities may behave differently during charging and discharging. A battery with a larger capacity may absorb more charge when it is charged and output more charge when it is discharged. This can cause smaller capacity batteries to overcharge and discharge, which can affect their life and performance. In the long run, batteries with small capacity may age faster and even be damaged.

Internal resistance difference problem

Different capacity lithium batteries usually have different internal resistance. In parallel, batteries with low internal resistance will bear more current, which can cause them to heat up more seriously and may even cause safety problems.

If the internal resistance difference is large, it may also cause the current distribution inside the battery pack to be unbalanced, affecting the performance and life of the entire battery pack.

Consistency problem

Different capacity lithium batteries may have differences in the production process, such as electrode materials, manufacturing processes, and so on. These differences may lead to inconsistent battery performance, such as charge and discharge curves, self-discharge rates, and so on. When used in parallel, these inconsistencies may affect each other, further exacerbating the instability of the battery pack.

Third, safety precautions

Try to choose the same brand, the same model, the same batch of lithium batteries in parallel to ensure that their performance and parameters are as close as possible to reduce potential risks.

Before parallel, each lithium battery is fully tested and screened to ensure its good performance, no damage, no leakage and other problems.

Use a professional battery management system (BMS) to monitor the charge and discharge process of the battery pack to ensure the safe operation of the battery pack. The BMS can balance the charge and discharge of the battery pack to prevent excessive charge and discharge of individual batteries.

In the parallel process, it is necessary to ensure that the connection is correct and firm, and avoid safety problems such as heating and igniting caused by poor contact.

Comply with the usage specifications and safety requirements of the lithium battery. Do not use the battery pack in a high temperature, humid, or flammable environment.

To sum up, lithium batteries of different capacities can be connected in parallel, but they need to be operated with caution and pay attention to safety. In practical applications, evaluation and testing should be carried out according to the specific situation to ensure the performance and safety of the battery pack.