alternator or battery 2003 cobra

[ron]

How can I tell if it's my alternator or my battery is bad. I think it's the battery but the guy at auto zone said it's my alternator. If the car sits a week or so the battery is low and the car barely starts. But after I drive it's ok . If the car idles for awhile that's when the battery gets low.The battery is the original thanks Ron could I put a volt meter on the car when it's running what should the volts be car has 27000 miles

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[Zack]

Put a motorcraft BXT-850 in there.
Is it the original battery?

 

[Dragon03]

volts with the car running should be between 13.5 to 14ish.......if you are below that I think your alternator is starting to take a crap on you....one more thing you might check are the fluids in the battery....my$.02 GL

 

[Cobratron]

I had the same issues last year with my original motorcraft battery. When I let it sit for a week it would barely start, but after i drove it was fine. I replaced the battery and it's fine now. Get a new Motorcraft same model and then get a battery tender.

 

[Venomblue22]

U can have a mechanical shop load test the battery for ya and if it fails, then u need a battery

 

[Aron]

Check the alternator with a voltmeter on the battery with the engine off and then running. If voltage checks out, pull the battery and have it load tested. My money is on a bad battery

 

[ShelbyGuy]

How can I tell if it's my alternator or my battery is bad. I think it's the battery but the guy at auto zone said it's my alternator. If the car sits a week or so the battery is low and the car barely starts. But after I drive it's ok . If the car idles for awhile that's when the battery gets low.The battery is the original thanks Ron could I put a volt meter on the car when it's running what should the volts be car has 27000 miles

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