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Bad battery vs. Bad alternator

Posted on 12/1/23 at 11:55 am
Posted by BilbeauTBaggins
probably stuck in traffic
Member since May 2021
4635 posts
Posted on 12/1/23 at 11:55 am
Car got jumped this morning and again at lunch. I let it run for about 45 minutes in the AM after jumping. About to take it to Autozone since I got the battery in April 2022.

What would confirm that it's the alternator and not the battery?
Posted by zbra24
Haughton
Member since Sep 2008
474 posts
Posted on 12/1/23 at 12:02 pm to
if you jumped it and ran for 45 minutes its not the alternator. If you have a multimeter you can test the battery yourself.
Posted by LEASTBAY
Member since Aug 2007
14326 posts
Posted on 12/1/23 at 12:17 pm to
Odds are it's the battery because batteries fail at a much higher rate then alternators. It's where I would start. Guess you will know once you get it load tested.
Posted by Dock Holiday
Member since Sep 2015
1641 posts
Posted on 12/1/23 at 12:26 pm to
You need to put a meter on the battery when the vehicle is running. Should be at or above 13 volts and less than 15.
Posted by BilbeauTBaggins
probably stuck in traffic
Member since May 2021
4635 posts
Posted on 12/1/23 at 12:47 pm to
Took it to Autozone. Told them it's been running for almost an hour without any changes and they went ahead and swapped since it's still within warranty time frame. Didn't even have to check if it was the alternator.
Posted by Clames
Member since Oct 2010
16638 posts
Posted on 12/1/23 at 12:58 pm to
quote:

What would confirm that it's the alternator and not the battery?



Bad batteries can kill alternators and vice-versa. A load tester and a DVOM will tell you what is wrong. It's a series of tests though, battery voltage under load, alternator supplied voltage/current under load and at idle and fast idle conditions, etc. An alternator can test fine while idling then be unable to adequately supply current while driving, which would cause the problem you are having.
Posted by notsince98
KC, MO
Member since Oct 2012
18076 posts
Posted on 12/1/23 at 1:55 pm to
alternator would mean your car wont run at all after a jump start. If you jump it and it runs fine until you turn it off, bad battery.
Posted by Miketheseventh
Member since Dec 2017
5823 posts
Posted on 12/3/23 at 8:57 pm to
The sure fire way to tell if it’s your alternator is take a voltage reading on the battery while it’s running. If it reads less than 13 volts then your alternator is bad
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