Balancing can be active or passive. In active balancing, the balancer circuit enables transfer of charge between different cells of the battery, i.e., transferring energy from cells with a higher charge to cells with a lower charge. The term battery regulator typically refers only to devices that perform passive balancing. A full BMS might include active balancing as well as temperature m.
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The individual cells in a battery pack naturally have somewhat different capacities, and so, over the course of charge and discharge cycles, may be at a different (SOC). Variations in capacity are due to manufacturing variances, assembly variances (e.g., cells from one production run mixed with others), cell aging, impurities, or environmental exposure (e.g., some cells may be subject to additional heat from nearby sources like motors, electronics, etc.), and c.
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