What could cause Battery to "boil"?

After driving a few miles my battery sounds like it is boiling inside and venting acid. What part could be bad now?

Thanks

Only two things---either the alternator regulator is overcharging the battery or the battery is bad.........take the battery to autozone and have it load tested...............Dan

old_coot said:

Only two things---either the alternator regulator is overcharging the battery or the battery is bad.........take the battery to autozone and have it load tested...............Dan

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Yup, stick a multimeter on the battery during idle. If it shows something crazy like 13.5 or more volts, the regulator built into the alternator is stuck and overcharging the battery.

eddie
'90 5-speed SC
'97 LX sport

Thanks. It is the third battery in 1 year. I'll bust out the meter tonight.

I think the voltage regulator is set in the mid 14's...You'll have to rev it up a little and measure the voltage to see if it is too high.

When the battery in my CTS did that, boiled the electrolyte, it was just the battery. It would only do it when the a/c ran and it vented water vapor not acid vapor. I thought the alternator was the culprit but the Caddy dealer said the alternator checked out and didn't replace it. It's been Ok ever since. But, if you've gone thru 3 batteries in a year, I'd definitely suspect the alternator was overcharging it.