Lithium battery balancing technology is the core module in the battery management system, which mainly solves the problem of internal voltage differences in the battery. The mainstream solutions are divided into two categories: active balancing and passive balancing.

Passive balancing mechanism

Passive balancing mainly relies on the resistance discharge method to release the power in the battery with higher voltage in the form of heat energy, thereby creating more charging time for other batteries. The power of the entire system is limited by the battery with the smallest capacity.
During the charging process, lithium batteries usually have an upper limit protection voltage value. Once a string of batteries reaches this value, the lithium battery protection board will cut off the charging circuit and stop charging.

The advantages of passive balancing are low cost and relatively simple circuit design, but its disadvantages are that it is only based on the minimum battery residual amount for balancing, and the capacity of batteries with less residual amount cannot be increased, and the heat released during the balancing process is completely wasted.

Active balancing mechanism

Active balancing achieves balancing by transferring power, which is more efficient and has less loss. Different manufacturers may use different methods, and the balancing current may also be different, usually ranging from 1 to 10A.
Passive balancing is more suitable for lithium battery packs with small capacity and low number of strings, while active balancing is more suitable for power lithium battery packs with high number of strings and large capacity.
For battery management systems (BMS), in addition to the balancing function, the formulation of balancing strategies is also crucial.

When selecting for actual applications, passive balancing is recommended for batteries with a capacity of less than 20Ah, and active balancing is recommended for medium and large battery packs above 50Ah.
For applications with a cycle life of more than 2,000 times, the life gain brought by active balancing can usually cover the initial cost investment. Special scenarios such as hybrid vehicles can consider hierarchical balancing design, using active balancing between modules and passive balancing within the module.