A: Lead and ... lead-oxide.
A lead acid battery is a galvanic cell between a base metal and its oxide (or, its 'rust' if you will).
Once the oxidation of a base metal starts to sink below its skin, then the oxidation process is like the self-fueling spread of cancer.
Watch out about polishing/etching off the anodization layer. That's like scraping off skin. In the above link, it is advised to apply a compound like Flitz, which likely hydrates the aluminum oxide layer, rather than thin it/ remove it with acidity or polishing activity.