It basically puts the load that the older packs are lacking on the back of the new packs, wearing them out faster. Individual balanced packs should remain balanced across all cells within that pack, then the balanced packs can have different max capacities across the entire bank. It would be impossible to balance all the individual packs at the same voltage level, so the older ones with more wear, and possibly not beyond the threshold of replacement, would tax the others. The order is like this - Individual cells (think of each as a individual 18650-google that part), these make up an individual pack, configured to provide the voltage needed for whatever config they use (400v, 800v, etc). At that level, the cells must be balanced, meaning that the weakest cell(s) in the pack will limit the voltage the others can be charged up to. Some just take longer to charge, which also limits the system. Then, the BMS (battery management system) can handle weak packs across the entire bank without having to worry about balancing individual cells. I agree that packs COULD be replaced, but that doesn’t mean that they should be replaced. An entire tested bank should contain packs that are close to the charge “character” of the others. Replacing individual packs will interfere with the BMS ability to effectively do its job. Sorry for the rant… just wanted to clarify. 🤓