Green Build-up on Wiring

[hellosailor]

"what difference does it make if the batteries had vented to this area "
I think the Fiat 124 or 128 series had a trunk-mounted battery, they became infamous for the trunk literally rotting out from the acid fumes the battery normally vents out. Mazda learned a lesson and used AGM batteries to prevent that in some similar models. BMW and Audi actually took to installing vent hoses instead.
Copper wiring does not like having battery acid, liquid, vapor, fumes, whatever, around it. And even in normal charging, there will be hydrogen emitted, and that can corrode the copper as well.