The two balancing methods are usually presented as a quality ranking, with active on top. They are not a ranking but a cost traded against a loss, and the review only closes once the series count of the string and the duty cycle of the household are both known.
What is being reviewed
Balancing keeps the cells of a series string at the same state of charge, so the string can run between its cut-offs instead of stopping at its first cell.
Passive balancing discharges the higher cell through a resistor, turning that energy into heat inside the enclosure. Active balancing moves charge from a higher cell to a lower one and keeps most of it in the pack.
Two boundaries belong at the front. Balancing does not correct a delivery whose cells arrived mismatched, because it works on the difference that remains after matching. Nor does it raise usable capacity beyond the weakest cell in the string; it only stops the spread widening.
Who wants which, and why
The pack designer prefers passive where the string is short and the spread small, because it needs no magnetics, adds nothing to the current path and cannot fail into a mode that moves energy the wrong way. The same designer prefers active where the string is long, because the energy burned in a passive resistor grows with the spread it corrects.
The service side wants whichever method produces a readable history, because an imbalance complaint is answered from a log.
Ask the supplier to name the balancing method in the specification, so the claim can be checked against a document rather than a conversation.
The owner experiences retained capacity and the frequency of imbalance alarms, both of which come from the interaction between the method and the installation.
Where the two sides disagree
They do not disagree about the physics. They disagree about which failure the buyer is accepting.
Passive balancing buys simplicity and pays in heat, in a balancing current limited by what the resistors can dissipate, and in the time at high state of charge the correction needs. Its failure mode is a spread that outruns the balancer.
Active balancing buys recovery and pays in components inside the current path and in cost, for a benefit that appears only when the spread is worth moving. Its failure mode is paying for capability the installation never uses.
Each side can produce a case where the other is wrong, which is why the argument repeats.
What the published specification says
Read literally, the published pages name the method on one model and leave it unnamed on the others.
Wording is quoted from the published product specifications, verified as of 2026-09; the word passive does not appear anywhere.
Two things follow. Active balancing is a published claim on exactly one model in the range, so a buyer comparing the others is comparing something unstated, and the two are not on the same basis. The phrase cell balancing is used without a method, which means it describes the function rather than the implementation.
The stack models add a second layer: their published architecture is master-slave with module-level monitoring, so balancing is resolved inside each module and the series count that matters is the one inside a module. A 51.2 V module is sixteen cells at 3.2 V.
When it matters
It matters most where the spread has somewhere to accumulate and little time to be corrected.
Long series strings are the first case: the penalty from a single low cell lands on the whole string, and the positions an outlier can occupy grow with the count. A stack of three or nine modules has more of them than a wall unit.
High cycling depth is the second, because cells that start a fraction apart diverge as they cycle, and the published cycle life figures are quoted at a stated depth of discharge.
Temperature spread inside the enclosure is the third, because modules at different temperatures age at different rates, and no balancing method corrects a thermal difference.
A delivery whose resistance spread approaches the balancing current is the fourth, and it is where the method stops being a preference. If the spread is wider than the balancer can absorb, the pack can pass its end-of-line test and report imbalance in service.
The reverse holds too: a short string, a shallow cycle and a tightly matched delivery leave neither method with much to do, and the difference appears in the bill of materials.
If the household runs deep daily cycles on a nine-module stack, the balancing method belongs in the specification review. When the same battery serves a shallow cycle, it does not.
The decision, and what stays open
The rule that survives the deadlock is to specify the method you can defend from a document, and to treat an unstated method as just that rather than as passive.
If active balancing is claimed, ask the supplier for four figures in writing before the order: the balancing current, the voltage difference at which balancing starts, the window in which it may operate, and how the function behaves at low temperature. Ruibit publishes the method on the model that advertises it and the general BMS description elsewhere, and none of the four figures appears on a product page, so they have to be requested rather than read.
Two items cannot be changed once the pack is designed. The balancing method is part of the pack's architecture, and changing it later is a different configuration rather than an upgrade, with the certification evidence and warranty terms attached to the first one. The series arrangement is fixed with it, which is why the count matters before the order.
At handover, record the cell voltage spread and the imbalance history. Balancing works on a difference, and that record is the only baseline for judging a later spread as normal ageing or as a balancer never sized for the duty.
FAQs
1. What is the difference between passive and active balancing?
Passive balancing discharges the higher cell through a resistor and turns that energy into heat inside the enclosure. Active balancing moves charge from a higher cell to a lower one and keeps most of it in the pack. Both keep the cells of a series string at the same state of charge so it can run between its cut-offs.
2. Does the published specification say which method a battery uses?
Usually not. In this range active balancing appears as a published claim on one model only, and the other pages use the phrase cell balancing without naming a method, so it describes the function rather than the implementation. The word passive does not appear in the published material.
3. When does the balancing method matter most?
On long series strings, at high cycling depth, where modules sit at different temperatures, and where the resistance spread of the delivery approaches the balancing current. A short string, a shallow cycle and a tightly matched delivery leave neither method with much work to do, and the difference shows up in the bill of materials.
4. Can balancing correct cells that arrived mismatched?
No. Balancing works on the difference that remains after cell matching, not instead of it. If the resistance spread is wider than the balancer can absorb, the pack can pass its end-of-line test and report imbalance in service. Nor can it lift usable capacity above the weakest cell.
5. What should be requested before ordering?
If active balancing is claimed, ask for the balancing current, the voltage difference at which balancing starts, the window in which it may operate, and how the function behaves at low temperature. Ask also for the cell voltage spread and imbalance history at commissioning, the baseline for later comparison.
