Originally Posted by
Alexv2024
Clearly the difference between 2 packs wired in series vs a whole single pack has some sort of effect, otherwise many people wouldn't notice this phenomenon. Not like the guys at SMC are inexperienced, clearly they know something about power systems.
There's definitely a significant difference in what the cells see in the 2 scenarios. Cells soldered tab to tab vs 2 connections (could be high resistance if dirty/loose) a bit of wire on top of the cell tab connections would look different under a big load.
That leads to some cells discharging more than others and could cause some to dip below 3-3.2v and get damaged.
End of the day if everything goes right, and you swap the packs so they arent in the same position, there shouldn't be a problem. But thats not always the case.
Adding resistance in series won't make certain cells discharge more than others. If there's no parallel path for the current to flow then the exact same current will flow through the cells.
The main advantage to pre assembled packs in series is that they can match cells that have comparable capacities and resistances. Unmatched cells can lead to unbalanced voltages. No 2 cells are identical due to manufacturing tolerances.