Uneven electrical current distribution in a parallel-connected lithium-ion battery pack can result in different degradation rates and overcurrent issues in the cells. Understanding the electrical current dynamics can enhance configuration design and battery management of parallel connections.
To meet the power and energy requirements of the specific applications, lithium-ion battery cells often need to be connected in series to boost voltage and in parallel to add capacity . However, as cell performance varies from one to another [2, 3], imbalances occur in both series and parallel connections.
Parallel Connection In a parallel connection, the batteries are linked side-by-side. This configuration keeps the voltage the same but increases the capacity. For instance, connecting two 3.7V 100mAh lithium cells in parallel will result in a total capacity of 200mAh while maintaining the voltage at 3.7V.
Six battery packs (each containing two cells connected in parallel, as depicted in Fig. 5) were tested using the method described below. For further reference within this paper, two parallel-connected cells are called a “cell group”. The current to each cell and the temperature of each cell were recorded.
The features of cell balancing in parallel connections are summarized. Recommendations of reducing cell imbalances in parallel connections is proposed. Uneven electrical current distribution in a parallel-connected lithium-ion battery pack can result in different degradation rates and overcurrent issues in the cells.
If the cost and risk don't warrant it then just parallel 4 batteries and hope for the best with a single BMS. The cells you put in parallel are no longer considered 4 cells in parallel but are now considered one cell with more capacity and able to source more current safely (if your bus is up for it.)