I'm not understanding where this thing is exactly, form the photo.
If IN the battery compartment could it be a tie down point for the batteries?
As for cleaning it.... I think you'd need some acid or chemical based thing to clean it.
What I would do is remove it, wire brush it/scrape it, then paint it. Depending on how it looked after brushing it, I might use one of those rust converting products before painting
naval jelly, ospho, or one of the many products such as Rust-Oleum Automotive 248659 Rust Reformer. Auto parts store will have it
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