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Why is calcium added to some lead alloys used in storage batteries?

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A labeled diagram of the periodic table entry for calcium, showing its atomic number 20, symbol Ca, atomic weight 40.078, electron configuration, and classification as an alkaline-earth metal. Icons indicate calcium is a solid with a face-centered cubic crystal structure and strongly basic oxides at room temperature. — calcium The chemical element calcium is the most abundant metallic element in the human body.

Calcium is added to lead alloys in lead-acid storage batteries primarily to improve the mechanical properties of the lead, such as its strength and hardness, as pure lead has relatively poor mechanical characteristics.1

In the context of automotive batteries, calcium is specifically used in the production of "maintenance-free" batteries. These batteries typically feature positive plates containing approximately 0.04 to 0.06 percent calcium and about 0.1 percent tin. By alloying lead with small amounts of calcium (typically 0.03 to 0.11 percent), manufacturers can create grids that are more durable and better suited for the demands of these battery systems.21