Battery cell charge imbalance

The Sunny Island battery inverter reports battery cells that hold different states of charge. It raises warning W948, or error F932 at a higher level, through its SiCom battery communication. SMA event 9315 calls this a battery imbalancing fault. It means the charge states of the individual cells differ too much. Cells in series drift apart in charge over time if they do not get regular equalization charges. This can reduce battery performance and lead to early failure of the storage system. Equalization charging brings the series cells back to a common state of charge. Check that it is set up with the cell voltage, absorption time and cycle time the battery manufacturer recommends. In the field, compare cell or battery voltages by position and track them over time. A spread between batteries that should be in the same condition points to a problem, but adjust the readings for temperature, discharge rate and age first. In flooded lead-acid batteries, differing acid concentrations are one condition that makes the Sunny Island recalibrate its state-of-charge value. If the imbalance fault persists, the installer should agree the next steps with the battery manufacturer.

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• sentence 5: support check: partial - Position and time comparison and adjustments are stated, but temperature, discharge rate and age are listed alongside voltage level; the passage doesn't directly say to adjust 'first' as field practice, a minor omission.
• sentence 7: support check: partial - Passage says contact the installer who clarifies next steps with the manufacturer, but does not mention the fault persisting as a condition.
• sentence 7: review: partial - Event 9315 says the installer must clarify next steps with the battery manufacturer, but nothing makes this depend on the fault persisting. -->