The engine compartment on my 2000 Focus has a nice plastic cover over the battery. Unfortunately this meant that whever I checked under the hood I didn't glance at the battery terminals. For some reason or another I recently had cause to lift the battery cover and was somewhat surprised to see a huge amount of battery terminal corrosion. It looked like something out of a science-fiction B-movie!
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At this point I wasn't sure exactly what the cause of the problem was, so I figured it was my fault for not checking the condition of the terminals more regularly. So I figured that instead of taking the car in and getting the problem fixed under warranty, I'd just clean the terminals myself. In fact, the problem appears to have been caused by a tiny crack in the battery's positive terminal allowing gas to escape and cause the deposits you see in the photos above.
Before I noticed this problem, there were no other symptoms of any kind. The car always started first time without any problem. However, once I got all the corrosion removed the car had trouble starting. A check with a voltmeter revealed that the battery voltage would fall to around 8 volts while the starter was engaged. It looks like cleaning the corrosion away somehow caused the battery to “go bad” although I'm not sure exactly how.
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While this maintenance is very simple to perform, please take note that you will be working on the electrical system of your car. If you are at all uncomfortable with this, or if you feel unsure of what you are doing, please do not carry out this work. Any modifications you make to your car are your responsibility.
If you have any corrosion on the battery terminals of your car, it is well worth getting it fixed before you find that your car won't start 100 miles from home on a rainy Sunday evening. It turned out that the cause of my corrosion was a crack in the battery terminal, but I understand that all batteries allow some gas to escape which causes this type of corrosion. Check your battery today!
1. Remove the battery cover by lifting the catch on the side of the battery.
2. Use a 10mm wrench or socket to remove the NEGATIVE battery lead:
3. Tie back the negative battery lead to ensure that it can't accidentally touch the terminal, then remove the positive battery lead:
4. Dissolve a few teaspoons of baking soda or baking powder in a couple of cups of water and pour the solution over the battery terminals to neutralize the acidic deposits on the battery terminals. Note that because my corrosion was so bad I did this with the battery still in the car, since I didn't want to touch the battery at this point. You may want to remove the battery from the car so that you don't make a mess all over the engine compartment.
4a. To remove the battery, use a 10mm socket to remove the battery tie down strap:
5. Use a battery terminal brush to remove any deposits from the battery terminal itself. Use a damp cloth to clean off any dirt and debris from the battery casing - an excessive amount of dirt can cause the battery to leak its charge.
6. Apply petroleum jelly or your favorite grease to the battery terminals. This will help to inhibit the build up of further deposits. I also purchased a pair of "anti-corrosion washers" for 99c from the local parts store. These a small felt pads that are supposedly impregnated with some chemical that helps to prevent corrosion.
7. Re-install the battery. Re-attach the POSITIVE lead first, then the negative lead. Check that the clamps are secure, then start the car to ensure all is well. Re-install the battery cover.
As it turned out, in my case the battery terminal clamps were quite badly corroded, so I ended up replacing them and the short ground lead that leads to the grounding point under the airbox. Some photos of the completed work, with the replacement battery installed:
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