Battery gauge voltage drop

Hey guys so driving home last night I noticed a drop on my voltage gauge. I think my battery is going is bad. I get to this conclusion based on the fact that when sitting at idle my voltage drops midway between 14 and 9, but once I get on the gas again it raises straight back to 14 and more. What do you all think?

Is your belt well tensioned? Maybe the alternator is not rotating as it should at low rpms.

I would look to the alternator and its brushes first.

I had the charging system checked today and my alternator failed the test three times. I ordered a new AC Delco one tonight. Hope the jeep keeps working until Friday night.

Lake919 said:

I had the charging system checked today and my alternator failed the test three times. I ordered a new AC Delco one tonight. Hope the jeep keeps working until Friday night.

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Throw a battery charger on it each night when you get home, and you should be good as long as you don't do any extended night driving.

I'm glad you found the problem, but for many years of XJ (Renix especially) the dash gauge is a notorious liar. It is poorly wired, and can drop drastically just when you turn on the heater fan, scaring you when there's nothing wrong. When diagnosing charging issues, always get the voltage directly from the battery.

I advise all to check the voltage with various accessories on, when all is healthy, so as not to have surprises. Once you know what to expect when, the gauge can be useful even when it is not numerically accurate.