ferret

car battery or alternator

30 posts in this topic

car wouldnt start the other night, checked the voltage to today it was like 11.2.  jumped the car with another running vehicle and the voltage went up to 13.6.  started the car and removed the jumper cables and the voltage dropped to 12.5 range. let it idle for about ten minutes, turned it off and it would not restart.  so bad alternator or battery?

Share this post


Link to post
Share on other sites
14 mins ago, ferret said:

car wouldnt start the other night, checked the voltage to today it was like 11.2.  jumped the car with another running vehicle and the voltage went up to 13.6.  started the car and removed the jumper cables and the voltage dropped to 12.5 range. let it idle for about ten minutes, turned it off and it would not restart.  so bad alternator or battery?

Probably battery.  While the car is running turn on the lights and check the voltage.

If the battery was already down and you jumped it it's not going to idle 10 minutes.  Especially if you turn on the lights.

Share this post


Link to post
Share on other sites

My battery died earlier this year.

Would supply "just enough" power to start cranking but that was all.

Got it started using a charger, but once it was stopped it wouldn't start again.

No warning light on dash because the alternator was working, but the battery wasn't able to hold a charge.

 

If you can jump start and it runs without a warning light showing on the console, it's most likely a dead/dying battery.

I ended up having the truck die in an auto parts store, so I picked up and installed the new battery there.

Nothing is as relieving as hearing a vehicle start right up! 

Share this post


Link to post
Share on other sites

I am so confused, disconnected the positive and turned on the high beams, radio, ac, wipers and everything, car still ran

 

battery is a costco interstate with a build date sticker 2/18, and the voltage never reached 13V while running (sign of a bad alternator)

 

hope the battery is still under costco warranty, that would be the cheapest place to start 

Share this post


Link to post
Share on other sites
2 hours ago, ferret said:

car wouldnt start the other night, checked the voltage to today it was like 11.2.  jumped the car with another running vehicle and the voltage went up to 13.6.  started the car and removed the jumper cables and the voltage dropped to 12.5 range. let it idle for about ten minutes, turned it off and it would not restart.  so bad alternator or battery?

should be around 14V running''sounds like alternator

Share this post


Link to post
Share on other sites

13.9-14.2vdc running would indicate a properly functioning alternator. Anything less would be a failing alternator. Good battery will hold about 12.5-13vdc off a fresh charge.

Share this post


Link to post
Share on other sites

Put an actual load tester on the battery, not just a voltmeter.

 

Whether it's the battery or alternator, the battery is in a weak state right now, so the reading will suck.  Fine.

 

Then give it good charge overnight, and hit it with the load tester again.  If it reads fine (12v-13v), but drops quickly once the load tester draws on it for 7 or seconds, then it's the battery.  If the voltage holds under that load test, and the battery starts the car up fine, but then does not test as well after a drive, it's the alternator.

 

We've come across many batteries that read just fine with a voltmeter, but hit them with the load tester, and the failure is quite evident.

Share this post


Link to post
Share on other sites

I had this same problem, and wanted to know if it was battery or alternator... 

 

 As previously stated, start the car, and while its running, disconnect the battery cables... if it keeps 

 running, that means your alternator works and is doing its job. 

Share this post


Link to post
Share on other sites

Physically check the battery for a date.  If its 5 year battery and its over 5 years old don't even waste your time troubleshooting as 9 out of 10 times the battery is shot.  Replace now before it gets cold.

Share this post


Link to post
Share on other sites

Battery was built 2/2018, interstate from costco, just called them and confirmed it's still under warranty, when I get back from FL, that will he the first step

 

After the replacement if it stil dont charge to 14V, ima do the alternator as well.

Share this post


Link to post
Share on other sites

start the vehicle, with the vehicle running disconnect the battery, if the vehicle stays running then replace the battery, if the vehicle dies then the alternator.  battery is designed for starting and running accessories

Share this post


Link to post
Share on other sites

Posted (edited) · Report post

I don't like to take off the negative cable with the car running.

modern cars have high electronics and need power for all it's operations.

taking off the cables could burn the computer.[old cars you could do that with the negative cable off not the pos]

also,in modern cars the draw is still there because all the electronics are "active" even when off.

load test is the best way to see the state of the battery.

I had mine tested once at auto zone,the battery was a 65 series  rated at 1000 cca and the load test said it was down to 440,the car still started even in the cold but dragged,i thought the starter was warning me,,nope,the battery was.

he tested the alt's power,it was rated at 110 amps[ex-police car] and it was peaking at 119 so,it was fine.

best way to see is go to have it tested free at advanced auto or auto zone.

HH

Edited by Heavy Hooksetter

Share this post


Link to post
Share on other sites

Have the "vehicle" tested professionally...Battery/starter/alternator can be tested IN their environment with proper equipment such as a Sun VAT 40.

A full system test can be done in 15 minutes by a good tech-no guessing.

 

For above posters that advocate disconnecting the positive battery cable to test the alternator...this was more "ok"? on vehicles of 30-40 years ago it was still a risky move but modern vehicles,heavily laden with sensitive $$$ ECUs numbering as many as 15-20 with can-bus systems and very hi output alternators,the ECUs do not like the AC spike to their components and you won't like what it does to your wallet.

Share this post


Link to post
Share on other sites

Pull the cables off the battery and you're guaranteed to blow a diode trio in the alternator (changes a.c. to dc) hence the name alternator. As said before 13.6 to 14.2 volts car running. Fully charged, a cranking battery trying to start the vehicle shouldn't drop below 9 volts, if it does, it's toast. I pull the wires on the plugs to keep it from starting right away.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to register here in order to participate.

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.