I replaced the battery on my 98 Mazda 626 GF 2L about a month ago. I haven't driven it for about two weeks, and noticed the voltage is down from about 12.57 to 12.02 so far.

I just noticed that white powder had formed on the bracket used to hold down the battery. The battery terminals are clean.

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I'm not sure when this started. I was worried about the battery running down due to it not being driven, so I did hook it up to my other car for about ten minutes to try and give it a little charge.

2 Answers 2


what you are looking at is corrosion caused by the gasses from normal battery operation reacting with the metal of the bracket. fix 1 (minimal) put 2 table spoons of "bicarb of soda" into a couple of liters of warm water and pour over corrosion, this will neutralize the acid and clean the area, gently hose around the battery and below with a garden hose to remove any other residue. fix 2 (upgrade) remove the battery bracket and paint with any oil based enamel, a spray can is cheap. this will prevent further corrosion by removing bare metal exposure as in your pic. car batteries usually run around 13.5v but will work fine at a bit lower voltage

  • Why say "bicarb of soda" instead of just "Baking Soda" ?
    – JPhi1618
    Commented Oct 20, 2015 at 14:02
  • 1
    @JPhi1618, I believe bicarbonate of soda is the common name for baking soda in some other countries. Either way, Rod, could you edit your response to include capital letters and punctuation? We strive for high-quality answers on this website. Yours has good information, but should be updated with proper sentences. Commented Oct 20, 2015 at 14:09
  • Strange, previous battery didn't have this problem. Commented Oct 20, 2015 at 17:00
  • Robert, your last battery didn't have the issue based on age of the parts. Your new parts have since lost its coating which is helping that corrosion to grow. I noticed that your battery looks wet in the cracks, possible the battery is leaking acid. Napa or other shops even Walmart sell a battery terminal cleaning can, It will also say with "Leak Detector". When you spray the battery to clean it, the yellow foam will turn pink/red letting you know that battery is leaking. The can of cleaner I'm referring to is what we use at my shop to clean the terminals, and to verify any battery acid leaks. Commented Oct 24, 2015 at 3:28

The white substance which you see around battery terminals is either lead sulphate or anhydrous copper sulphate . Anhydrous copper sulphate changes to blue colour when water is added to it. The bluish substance which you see around corroded copper terminals or copper clamps is hydrated copper sulphate.

Cleaning Corroded Battery Terminals:

To clean lead sulphate or copper sulphate from terminals, first disconnect terminals from battery. Make sure, you are wearing gloves as these chemicals can affect the skin. Now, wash terminals with clean water. If rust washes away, then no more hassles. Otherwise, wash them with the solution of any of these bases caustic soda, washing soda or baking soda made by dissolving base into water. Simply dipping battery terminals or clamps for few minutes into solutions of these bases also works. After cleaning with base solution, wash terminals again with clean water to clear away the remnants of base.

It is advised not to pour the solution of any of these bases over battery posts to clean them as it might gain access to battery interiors through vents, joints or leaks. If entered, it can badly affect the performance of battery. Instead, use a cloth dipped in base solution to clean them or use a brush to rub the rust off. Take extra precautions while cleaning hydrated copper sulphate which is bluish in colour because it is poisonous.

Prepared solutions are also available in markets to clean the corrosion. You can also use them.

Prevention from Corrosion:

1- Corrosion can occur in dry environment but it is boosted by moisture and salts present in water. Therefore, keep the batteries away from moisture and damp places.

2- Do not wash interior of car engine bay with water. Water increases speed of rusting metallic parts of engine bay which are not covered with paint and also joints of power cables and battery terminals.

3- Always keep the battery top dry and free from dust and other pollutants. After pouring water into flooded lead acid battery, never forget to dry the surface of battery. Close the caps of individual cells tightly.

4- Apply Petroleum jelly or grease to battery terminals to protect them from corrosion.

5- Use clamps and battery terminals made from good quality copper which are also alloy plated. Layer of alloy prevents terminals from corroding.

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