Found this on my OEM battery last week, just before the snow.
Finally warmed up enough to do something about it yesterday.
The shop vacuum managed to pick up most of it that wasn't trapped under the strap.
Pulled the battery and scrubbed everything down with baking soda to a fairly good surface.
Only a little flash rust before two coats of satin black Rustoleum.
The sunroom made it up to about 80F so it dried pretty quickly.
Got a new NAPA battery just because.
The 6 year old Panasonic developing incontinence did not give me good feels.