Contamination from galvanized iron

Zinc is used as the negative electrode material in aqueous primary cells because it has a high energy density. However, Zn is prone to corrosion, particularly when certain impurities are present, that can result in decreased battery life and compromised performance. A common contaminant is iron. When it comes into contact with the Zn and becomes galvanically coupled with it, hydrogen gas (H2) will form at the iron surface from the reduction of water in the electrolyte. Zinc is oxidized and dissolves into the electrolyte as zincate or precipitates as ZnO. 

---