What is the difference between active balancing and passive balancing in BMS systems?

If the lithium battery pack is a wooden barrel, and the battery cells are the wooden boards that make up the barrel, due to the manufacturing process and usage losses, the wooden boards of the barrel become uneven in length and length.

Passive balancing refers to sawing all wooden boards short according to the shortest length. This method is simple and efficient, but the remaining water (capacity) in the barrel decreases. (Passive equalization uses a resistor heating and discharging method to consume the "excess power" of high-capacity batteries, thus achieving the goal of equalization.)

Similarly, for this bucket, active balancing involves taking the sawn leftover materials to make up for the missing wooden boards to achieve consistency. However, this method is cumbersome and inefficient, but there will be much more water left in the bucket than passive balancing. (Active balancing is the process of transferring excess electricity to cells with high remaining capacity through energy transfer, ensuring consistent battery consistency.)