Q: Battery terminal corrosion on 2005 Mercury Montego

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Postive battery terminal corrosion cleaned month ago.
Corrosion returning.
(1) Answer
The battery probably has a small leak, possibly around the battery terminal. I would consider replacing the battery. Also, when you clean a battery, clean the entire battery with an acid neutralizer (baking soda) and remove both terminals and clean the posts and the cable ends.