Passive and active are different mechanisms
Passive balancing bleeds charge off the high cells as heat. Active balancing moves it to the low cells. The distinction matters for large packs, where bleeding the difference away is both slow and thermally awkward.
The three inputs
Cell matching sets how fast drift appears, capacity sets how much charge has to move to correct it, and duty cycle sets how much time is available to do it. A pack that is idle overnight has very different requirements to one cycling continuously.
- How well matched the cells are in capacity and internal resistance
- Pack capacity, which scales the charge that must be moved
- Idle time available for balancing to act
- Enclosure thermal headroom
Balancing does not rescue a bad pack
A cell that is genuinely failing will drift faster than any balancer can correct, and higher balance current only hides the symptom for longer. Persistent drift after balancing is a cell problem, not a BMS problem.
Official next steps
Frequently asked questions
Passive bleeds charge off high cells as heat; active moves it to the low cells.
No. It helps where drift is fast or idle time is short, and adds heat everywhere else.
No. Persistent drift after balancing indicates a cell problem.