What battery cell-voltage spread tells you

Calculate a spread from one coherent sample

Subtract the lowest reported cell voltage from the highest in the same pack and sample. If the highest is 3.340 V and the lowest is 3.320 V, the spread is 0.020 V, or 20 mV. This example does not define a good or bad threshold.

Do not mix the highest reading from one minute with the lowest from another. Keep pack identity, timestamp and the number of cells represented. A bank-level voltage divided by an assumed cell count is not individual-cell telemetry.

Check resolution before admiring precision

The reporting protocol limits the precision available to the dashboard. If a device supplies coarse voltage steps, a display with extra decimal places cannot create finer measurement. Likewise, rounded values may make two cells appear identical even when the underlying difference is smaller than the reporting step.

Sunstead can show cell readings only when a supported BMS connection actually supplies them. The precision depends on that protocol and equipment. Absence of cell data is not evidence that the cells are balanced.

Record what the battery was doing

Charge state, current, temperature and recent operation give context to a spread. A value during active charging should not automatically be compared with one from a resting pack. Manufacturer guidance may focus on particular operating conditions when evaluating balance.

Victron’s battery troubleshooting manual treats cell imbalance in the context of that battery’s behavior and procedures. It is useful evidence that diagnosis is conditional; it is not a set of thresholds or recovery instructions for a different battery.

Build a short comparison record

Repeat at comparable operating states. A pattern that persists is more informative than an isolated screenshot. Record missing values honestly; do not fill them from another pack to complete the form.

Use the manufacturer’s next step

If a warning occurs or a repeated pattern concerns you, retain the record and follow the exact battery manufacturer’s support procedure. Do not alter cell-protection or charging limits simply to reduce the displayed spread. A quieter screen would not establish a healthier battery.

Also distinguish an electrical issue from a telemetry issue. An impossible cell count, wildly inconsistent units or a discrepancy with the supported manufacturer view may need a protocol investigation. Report both views at the same time if possible.

The useful conclusion is specific: “this pack repeatedly reports this spread under these conditions,” followed by the applicable documented interpretation. Avoid reducing the entire battery’s health to one unlabeled minimum–maximum value.