Car Talk

April 2006

Dear Tom and Ray:

I own a Burgundy (I know that's important) 1992 Honda Accord. About six months ago, I couldn't get the car to start. Looking under the hood, I discovered that the clamp on the positive battery cable had completely corroded away. I made a quick fix with a hose clamp, but figuring that was only a temporary solution, I took the car to my local dealer and had the entire battery-cable harness replaced. Yesterday, I went to give someone a jump-start and discovered that the new battery-cable clamp on the positive side had turned to mush. It is literally liquefied, and appears to be melting away. It was also completely covered with a mound of bright blue-green, powdery material. What's going on? Oh yeah, the battery is only about a year old. -- Joel

RAY: Your battery has acid reflux, Joel. You need Prevacid.

Beat up old car

TOM: The blue-green powder you're seeing is the corrosion that results when the acid in the battery meets the lead and copper of the connector. I happen to have a Ph.D. in chemical engineering, Joel, so I can tell you precisely what's happening here. The H2S gas from the battery combines with the PB and CU of the clamp and the O2 in the air, and produces H2SO4 (sulfuric acid), hydrogen and a blue-green version of Aunt Jemima pancake batter.

RAY: What's the chemical formula for Aunt Jemima's?

TOM: I'll have to check my CRC Reference. But the mystery here is why the battery is releasing gas. Modern batteries are sealed, so they're not supposed to out-gas at all. But they do have vents so that if the pressure inside gets too high, they release gas instead of exploding.

RAY: One possibility is that your battery has a bad cell. Even though it's only a year old, that happens.

TOM: But a more likely explanation is that your battery is getting overcharged by the alternator.

RAY: I'm betting that when you went to the dealer, you just told him what to replace -- you didn't let him diagnose the problem. We call that tendency "male answer syndrome." My brother and I have both been in therapy for it for years now.

TOM: If you had, instead, just gone in, shrugged your shoulders and pointed at the melted terminal, he probably would have done a real diagnosis and tested your charging system. That's what he needs to do now. Testing the charging system will tell him whether the battery is bad, if it's getting overcharged, or both.

RAY: In any case, we're pretty sure that you're going to be overcharged, Joel. But the jury is still out on the battery. Good luck.

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