Can batteries of same voltage but different capacities be connected together?
It's generally recommended to use batteries with matching capacities and matching voltages when connecting them in series and/or in parallel to ensure optimal performance and longevity. Overall it's technically possible to connect imbalanced batteries together, but the capacity mismatch can lead to performance issues and potential imbalances between the batteries.
In a scenario with a 15Ah battery combined with a 20Ah battery in series, the overall capacity of the battery pack will be limited to 15Ah, despite the larger capacity of the 20Ah battery. The lower capacity battery may discharge faster than desired, and it may reach its minimum voltage level earlier than the larger capacity battery. This can result in uneven usage and potentially cause imbalances between the two batteries, leading to performance issues and reduced overall runtime.
When imbalanced batteries are connected in parallel, the voltages of the batteries should match, but the capacities can be different. When lithium-ion batteries are connected in parallel, their capacities are effectively combined, resulting in a higher overall capacity. This means that if you connect a battery with a capacity of 100Wh in parallel with a battery of 200Wh, the combined capacity of the two batteries will be 300Wh.
However, when connecting batteries of different capacities in parallel, the batteries will not discharge or charge at exactly the same rate. The battery with the higher capacity will contribute more to the total energy storage, while the battery with the lower capacity may reach its limits sooner.
Technically possible, but with issues
Both methods, combining in series or in parallel, can lead to potential issues such as imbalanced usage due to imbalanced charging and discharging rates, which can cause strain on the batteries and potentially reduce their overall lifespan.
To mitigate these risks, we recommend to only use batteries of similar voltage, capacity, chemistry, and age when connecting them in series or in parallel. If you still wish to use the batteries in series despite the capacity mismatch, it is crucial to monitor their voltages closely and ensure that they are not over-discharged. Additionally, using a battery management system (BMS) can help monitor and balance the charging and discharging processes to ensure the safe and optimal performance of the battery pack.
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