Overview:
When it comes to battery balancing, it's generally true to talk about the benefits of extending battery life. But it's still necessary to explore and improve this problem in the real world.
1. Why do you need battery balancing?
Simply put, a series of battery packs, no matter how you filter, there will always be an imbalance. Thus, in actual use, the output capacity of each series is different. 
"Cell Balancing Techniques using the example of Li-ion battery system for the opel Ampera"
The battery has not only the limitations of overdischarge and overcharge, but also the input and output power at different temperatures and different SOCs. That is to say, the limitation of a single battery will affect the entire battery.
Note: This is not equal to a single overrun, it is equal to the whole unsafe, but the battery will be damaged, and the problem of persistence will occur. 
Figure from "VOLTEC Battery System for Electric Vehicle with Extended Range"
Of course, the most important thing is that the battery packs connected in series also follow the Matthew effect. Because the load is consistent, the weaker (self-discharge, low capacity, hotter) battery will always bear the greater pressure. (Stress), then in a battery pack, the battery will age faster.
(Please read the PDF for details)
Auto Transfer Switch,Automatic Transfer Switch,Emergency Transfer Switch,Automatic Changeover Switch
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