Battery or Altenator?

Old 12-21-03, 01:18 PM
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Arrow Battery or Altenator?

My friends car always needs a jump. It always starts with a jump. Its seems to me its the altenator because its supposed to keep the battery charged. The green eye on the battery is gone.. which tells me the battery is dead. Hmmm. I am confused can sombody tell what else I can do to tell if its the battery or the altenator? PLEASE!!!...
Old 12-21-03, 01:40 PM
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First thing you need to do is replace the dead battery and then check voltage at the alternator. You can not do a voltage test and get conclusive results with a dead battery. Depending on the reading you get there will tell you what to do or where else to look.
Hope this is helpful to ya,
Old 12-21-03, 01:59 PM
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What Make, year etc, How old is the battery?
Old 12-21-03, 02:50 PM
mike from nj
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correct, an alternator will charge a battery that is good (able to be charged)

a bad battery, an old battery, one that's been dead for a while, or just a cheap $29.99 battery has seen better days.

try to measure the battery voltage while it's running. this will help your diagnosis of the alternator vs. battery.

let us know what you find
Old 12-21-03, 02:53 PM
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99 Toyota Corolla

I am not sure how old the battery is but the liquid inside is about an inch from the top, and its in good shape/Clean. Its the kind you cant fill with liquid.
Old 12-21-03, 02:56 PM
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I would suspect battery let me explain. The green eye is not there with indicates a problem. The car runs once jumped with means the alt is giving voltage.
Go to radio shack buy a cheap DVOM meter and measure the voltage on the battery posts on the DC scale of the meter.(do this with car running).You should see about 13.5 volts. This is the voltage the alt is putting into the battery.
This is not saying the battery will hold it just what it is receiving.
Also if the battery is 3 or more years old it is toast.
And besides once a battery is dead it never fully recovers and is damaged.
Running the car with a dead battery is not good for the alternator because on a good battery once it is charged the alt just maintains it.
So the Alt shuts down its supply of juice till battery requires more.
with a dead battery it is always on charging and keeping the car going.
in addition the battery is kind of like a shock absorber for your electical load it takes high amp demands a lot better then the alt it has lots of reserve power for all those high demand items like light blower motors etc.
Old 12-21-03, 04:37 PM
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I would add 1 think to that advise. Do you alternator testing AFTER replacing the battery. You can't get a reliable voltage reading with a bad battery. The battery has to be good before testing the alternator.
Old 12-21-03, 04:48 PM
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keep this in mind

Keep this in mind 99 corolla is a computer car if battery and alt were shot car would not run at all.
I would go with the battery ASAP you are going to fry the alt and they are not cheap.My son has a 99 rolla good car take care of it and you can get 200k miles easy.

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