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Old 08-03-2021, 11:15 AM   #1
Kolusion
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Question Defective battery?

Hey all

I have a problem where my battery warning light comes on and the alternator stops charging. I have confirmed the alternator stops charging when the battery warning light comes on by checking the voltage on the battery terminals using a multimeter. With the engine running, I get 14.55 volts when the battery warning light is off and about ~12.6 volts when the battery warning light turns on, and the ~12.6 volts decreases to bellow 12 volts in less than ten minutes. I also further tested the alternator when the battery warning light was on by disconnecting the cable from the alternators B post and measuring the voltage which was a jumpy ~3-~7 volts.

I replaced the alternator (twice), the crankshaft pulley and the drive belt. It made no difference. Now I'm wondering if it's the battery.

I just ran some tests:

Test 1: I started the car with all the accessories off and let it run. Fifteen minutes later I turned the headlights on, then ten seconds after turning the headlights on, the battery warning light turned on and the alternator had shut off.

Once the battery warning light comes on and the alternator stops charging, I need to let the car sit for 24 hours for the problem to go away, so after 24 hours I ran another test...

Test 2: I started the car but this time I turned on the headlights straight away. This time it took only two minutes for the battery warning light turned on and the alternator to shut off.

After 24 hours I did another test. For reference, the ambient temperature was 12 degrees:

Before cold start: 12.25 volts
After letting the car run for two minutes and then turning it off: 12.51 volts
Thirty five minutes after turning the car off: 12.32 volts

Afterwards, I pulled the battery from the car and put it on the charger and charged it to 100%. Once the battery was floating at 100%, I disconnected the charger from the battery and measured the battery voltage with a multimeter. I got 13.07 volts. One hour later I got 12.91 volts, three hours later I got 12.85 volts and nine hours later I got 12.82 volts.

I don't know much about electricity but the battery voltage looks good, however, I'm wondering if the battery is not delivering the amps in the current and sufficient current is not getting to the alternators' regulator, causing it to shut down, if that makes sense.

As can be seen by comparing my first two tests, placing a load on the battery induces the problem faster. This tells me the battery is not taking the charge from the alternator and therefore the battery is defective.

What do others think?

Last edited by Kolusion; 08-03-2021 at 11:48 AM.
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Old 08-03-2021, 12:08 PM   #2
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Re: Defective battery?

Sounds like you may have a bad cell. I don't know about Australia but autopart stores in the US will load test the battery out of the car. How old is the battery?
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Old 08-03-2021, 12:39 PM   #3
Kolusion
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Re: Defective battery?

A bad cell is what I was thinking too. Yeah I could probably take it to an auto store and have it bench tested but I'm pretty sure its the battery.


The battery is two years old, and we had a 4 month lockdown here in Melbourne last year in which I drove the car only once every two weeks, so perhaps I let it run down too low and it did some damage.
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Old 08-03-2021, 01:34 PM   #4
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Re: Defective battery?

A static test can only tell so much. Like you said you need to get it load tested.
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Old 08-03-2021, 01:37 PM   #5
Kolusion
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Re: Defective battery?

Why do you think about test 1 and test 2? The harder the load, the fast the battery warning light turns on and alternator shuts off and then the car needs to rest for 24 hours before everything is working again..... that has to be a bad battery don't you think?
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