Today: Why buildup on you car's battery posts could be the sign of something serious.

Dear Car Talk

Dear Car Talk | Mar 01, 2008

Dear Tom and Ray:

There is a fluffy white/blue deposit at the base of the positive-terminal post of my battery. The service manager's explanation is: This is perfectly normal for a sealed battery. When a battery is charged, gas escapes from a small gap between the post and the battery case and forms the deposit. The service manager recommended "corrosion treatment" for about $20. Are all batteries designed this way? Is this corrosion treatment worth it? -- Art

RAY: We see a lot of batteries with a little bit of corrosion at the terminals. But if there's a lot of buildup there, it could signal a problem.

TOM: Right. Batteries and charging systems that are functioning properly don't create mountains of whitish-blue crud on battery terminals.

RAY: So you could pay this guy $20 to take care of it for you. Or, if you prefer, you can clean it up yourself. You just mix up a cupful of baking soda and water, to the consistency of watery pancake batter.

TOM: Then slather it all over the terminals. It attacks the corrosion, and then you wash it all off with a hose or a bucket of water.

RAY: We also use a spray you can buy at an auto-parts store that coats the clean terminals and prevents the corrosion from coming back -- kind of.

TOM: If there's something wrong with your battery or charging system, the corrosion will come back despite the spray. So, then you'll need to investigate.

RAY: The most likely culprit is an alternator that's overcharging -- like we do all the time at the shop -- and causing your battery to out-gas.

TOM: So, Art, I'd clean off the terminals, re-secure the connections and then keep an eye on it. And if the stuff comes back in a couple of months, put the 20 bucks you saved toward a complete charging-system check.

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