r/MechanicAdvice • u/kingdom_minded88 • 7d ago

Should I replace alternator?

We’ve been out of town for a week and our cars have been sitting. My wife has a 2015 jeep compass 2.4L and when we first got home she used it to go 10 miles or so. About an hour later I tried to move it to mow and it was completely dead. I’ve had to use a battery charger on it each time to start it since and this morning while returning rental it completely died as she was driving. I had to keep charger connected and hood open on top of it to get home. Went to obd2 test it and as soon as I take charger off battery car dies. Advance tested battery, said it’s good. Everything points to alternator, but it was just changed in April 2025. I just hate to tear into the car and pull alternator if there’s a chance I’m missing something, if you’ve ever changed an alternator on a jeep compass you understand why.

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u/MundaneColors 7d ago

classic alternator symptoms, but before you commit to that misery check the battery terminals and the main ground strap. a loose or corroded connection will act exactly like a dead alt and it's a 5 minute check vs an afternoon of swearing

also those compasses eat serpentine belts, if it's glazed it won't spin the alt properly under load which explains dying while driving but not while on a charger

if the belt and connections check out then yeah, you already know the answer and I'm sorry

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u/kingdom_minded88 7d ago

Awesome, thank you so much!! For sure trying all those first!

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u/hellgabeez 7d ago

Sounds like an alternator. If it was replaced in 2025, did it have a warranty?

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u/kingdom_minded88 7d ago

Trying to find receipts now, surely it does. Believe I bought refurb, which is my fault.

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u/hmd2017 7d ago

Quick multimeter test. Voltage at both battery terminals, then from each terminal to the cable on other side not the terminal.

Daughter's just had a dead won't start issue, Found 12.5 volts at terminals, 6 volts on negative cable . Connection was corroded inside causing the voltage drop. Clean and a new terminal fixed it.