DIRT ON BATTERY on 1991 Mazda Protege

TODAY, I SAW DIRT ON POSITIVE CONNECTION, ON BATTERY, THE CAR RUNS WELL,I WANT TO KNOW WHERE COULD THE RESIDUE COME FROM?
ANITA

Get Your Car Fixed at a RepairPal Certified Shop.
We certify shops based on expertise, quality work, and verified customer reviews
1 answer
This is called corrosion buildup from the battery acid, this will cause resistance in circuit and may lead to car not starting, needs cable end removed from battery and cleaned and then reinstalled with good clean connection and retension.