What may result if water is added to a nickel-cadmium battery when it is not fully charged?

• A. No adverse effects since water may be added anytime.
• B. Excessive electrolyte dilution.
• C. Excessive spewing is likely to occur during the charging cycle.
• D. Increased charging efficiency.

Answer: (C)

During charging, nickel-cadmium cells produce hydrogen and oxygen gas as the electrolyte is electrolyzed. If water is added while the cell is still charging, especially when the cell isn’t fully charged yet, the increasing gas pressure can push electrolyte out through the vent. This “spewing” happens because the combination of ongoing gas generation and a higher liquid level from the added water raises the internal pressure and ejects electrolyte. That’s why adding water during charging is discouraged; it doesn’t improve charging efficiency and can actually cause loss of electrolyte and venting. If water is needed, it’s best to add it after charging is complete and the cell has cooled, to avoid disturbing the cell while gas is being produced.