The corrosion can be neutralised by scrubbing the corrosion with a small brush (old toothbrush works fine) dipped in a solution of sodium bicarbonate. Once the residue has been washed away with clean water and fully dried, apply a smear of vaseline (petroleum jelly) to both terminals to prevent further corrosion. If it was really bad, suggest removing both terminals (negative first) and making sure mating surfaces are shiny before reinstalling (negative last). You'll need your radio code.
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'98 N/A S70 184,000Klm