Alternator and battery suddenly died- why?

[Brofessor]

Went to start my car around 11PM Sunday night, not even a click. Dome light very dim, but still came on. Didn't check other accessories. I called AAA for a jump, which got the car running fine until I turned the headlights on. Tow guy had a multimeter and told me the battery was reading only 4.6 volts- apparently the alternator wasn't charging.

Today the shop says the battery and alternator are both bad and need to be replaced. Alternator is 111k miles and original. Battery is an Optima red top 34r that was bought almost exactly two years ago.

Here's the weird part. I drove back from work (had to use the printer) at 1:45 AM ish Sunday with no idiot lights or signs trouble what so ever. Car sat parked between then and 11pm.

Car is a 1990 Nissan 300zx that sees mostly short trips, but is driven for at least half an hour per day, mixed freeway and city, which I was under the impression was enough to keep things charged up. Headlight dimmed sometimes at very low rpm but the car has had some idle issues. It had been raining a lot so the alternator could have got wet, and my P/S leaks near it but not on or over it.

I've had alternators go out and batteries quit, but never both at the same time with no warning. Why/how does this happen? Thanks!

 

[eljefino]

Could be a diode went in the alt, shorting the battery. Has anyone tried a long 6-10A charge on that battery to see if it'll come back?

 

[Colt45ws]

Alternator went bad and nuked the battery. Its not uncommon.

 

[Audi Junkie]

A bad batt can kill an alt.

 

[Colt45ws]

Thats true as well, though it was only two years old. Alt is original, so it might be more likely, though it is an Optima battery, so maybe?

 

[aquariuscsm]

I use only Die Hard batteries. My current one is a Die Hard Gold. That would be my battery recommendation.

 

[Michael_P]

Check the cables too. Not as likely of a problem as others mentioned, but I have seen this baffle several people. Oxygen on the copper causes resistance.

 

[mrkdk]

the battery went bad and damage the alternator.this is very common. Optima battery will have a short life if the voltage regulator is not set up for them. they will always be under charged in most systems unless they changed for AGM batterys.

 

[Brofessor]

Thanks folks! Shop guy said he carries Interstate but he can get whatever battery the customer wants. I've got some warranty left on the Optima according to the receipt I saved, but it's not going back in this car. The reason why I chose the red top was not having to clean the negative terminal so much- kept corroding with the last Napa battery even with felt donuts and dielectric grease.

Though, if the battery and alt were bad, how was it possible for the car to start and run fine to get me home, but not start or run 16-17 hours later?

 

[mechtech2]

They may both be bad, of course.
We know the alternator is bad for sure.
Is the battery really toast?
who knows?

 

[oilboy123]

Originally Posted By: Brofessor
Thanks folks! Shop guy said he carries Interstate but he can get whatever battery the customer wants. I've got some warranty left on the Optima according to the receipt I saved, but it's not going back in this car. The reason why I chose the red top was not having to clean the negative terminal so much- kept corroding with the last Napa battery even with felt donuts and dielectric grease.

Though, if the battery and alt were bad, how was it possible for the car to start and run fine to get me home, but not start or run 16-17 hours later?


I started getting the Red top for the same reason you did.
I went and got about 5 Red tops in the family fleet.....it's a failed experiment. Their warranty that the offered me is not worth my time either. I might try another AGM battery in the future, but it won't be an Optima......

My bet is alternator or battery.

 

[CharBaby]

Originally Posted By: Colt45ws
Alternator went bad and nuked the battery. Its not uncommon.


+1

 

[mrkdk]

battery post must have the acid neutral if corroding had strated.clean post and wire with baking soda and water,soda or battery cleaner spray. just cleaning with brush will not work.

 

[frmtbiker]

When either the alternator or battery dies, if you dont catch it, they often take the other with them.