When I was about to leave for work today, my car was dead. It would not even turn over. So I had my friend jump my car and when it was jumped, my car started up fine, but my battery wont stay charged for some reason. While im driving it, the light still flashes and makes this buzzing noise in my dash. When I go park it and let it sit for like 30 min, the battery is dead again. Is it my alternator that has gone bad or is it just my battery? Please help, I need to get this back on the road.

86 Trans Am 4bll

 

Hmm... might be both actually. I had an alternator go bad and my battery got run all the way down several times and my battery end'd up dieing to. Call to a local autoparts store (Autozone, advanced auto) They will probably test it for free. Pretty much slap a machine on alternator output have you crank the car with the coil unpluged or pedal to the floor so it won't start. And it reads how much volts your alt is putting out. I'm sure they can test batteries too.

 

Got to pepboys and have them test the alternator, the battery, and the starter at the same time. I say this becuase I had the same problem as you. My problem was the starter killed the battery which inturn made the alt. work to hard and by the time the alt. died, the new battery was getting ready to die again. After replacing the starter all my problems went away. At least this way your not pulling your hair trying to figure out the problem.

Hope that helps.

 

That makes sense too... I replaced my starter about 1 month after the alternator another month the battery died.

 

Sounds like your Alternator isn't doing it's job anymore. Like said above, go get it bench tested.

 

chances are it isn't the starter unles it was the cause in the first place.

if you have a multimeter, you can put it on the battery terminals, should be above 12 volts. you can test the alternator by having the car running, unhook the battery cables, if it dies the alternator is junk. You can even hook up the multimeter to the alternator, it should be dishing out 13+ volts, make sure u give the car a good rev before u try it, sometimes if the pulley is off or the bearings in the alt don't get a good spin from the belt, it will read low.

Or if you have the time, like said take it to your local autozone/advanced. they do that for free. But if you like me, nothings around you (even a Mcdonalds, and you know theres a mc-e-d's around every corner!!!)

 

same thing happened to a friends sunfire about 3 weeks ago. It was simply an old/dead battery.

If the car runs fine when you get a jumpstart, the alternator is likely okay (cause it's running everything). But if you drive it around for too long with it futily trying to charge a bad battery, it will wind up working too hard and badness will ensue...

I'd have PB check the battery and the alt (just in case - since they do it for free), but I'd put a 5 spot on the cause being a bad battery :P

 

just fyi, if the alternator goes; it's about an 80% chance the battery will need replacing too.