Hi guys. I bought the battery to O'Reilly and they charged the battery after confirming the battery was good. When they charged it, I re-installed it and the car started right away. I bought the car back to O'Reilly and they tested my alternator and said it was bad. At the moment, my car is at the shop and they will confirm if indeed its the alternator. But for my car to sit for 1 day and the battery is drained is not right. But the alternator test with O'Reilly failed so that is currently where I am.

 

My alternator was diagnosed at an autozone which also gave the same reading so sounds about right! And my battery did the same as well so you are not alone -> I jumped my car probably every morning before going to work for a week since it would die overnight when i had the bad alternator. Best part was -> my car randomly shut off on my while I was driving on the high way so I was coasting with no power for a few seconds sooooo alternators are no joke!

 

Yep. This just happened suddenly so since changing the battery in late June, this is the first time this happens. So hopefully they confirm what O'Reilly confirmed. If so then they will change it. I have an extended warranty which covers the alternator.

 

Okay guys. So i just got a call back from the shop and they stated that they tested it and the battery and alternator tests passed!! So O'Reilly's test was a fluke?? There is a reason why my car did not have any lights at all this morning because of a battery that was reading 6 VDC!! This is crazy!!

 

Had similar happen to mine. Charging test was fine but it drained battery when not in use (destroyed a new battery in about 6 months). Auto electrician said alternators in our cars especially sensitive to jump starting etc. No probs since replacing alternator

 

Yep. I told the dealer to change it but they said they cannot change it under the warranty as long as it is passing. I know its the alternator. My only saving grace is that it does it when they test it tomorrow.

 

I highly doubt it is the alternator. My money is still on a bad battery.

 

Okay. Even though the battery is 4 months old barely? The auto parts store and dealer tested the battery as good.

 

Here's how I'm looking at it...
An alternator charging test (if you know what you're doing) is definitive...the alternator is either charging correctly or it's not.
With the battery test, if it has a bad cell, it can test perfectly fine when the cell is not shorting. Once the cell is shorting, then it will fail the test.
So, in my opinion, the battery test is not definitive. It's a way to test for other issues with a battery besides a bad cell.

I recall previously you mentioned that you checked the battery at 5.8V before you took it out and to the shop, where is read 10V.
Voltage doesn't magically appear, unless when you checked it the cell was shorted out, and the trip to the shop returned it to a normal state, and then it tested 10V.
The shop that said the alternator was bad, did they give you any readings as to alternator output at idle or under load?

 

Get the shop to test current draw when car is off. After about 3mins (with key fob away from vehicle) should be down to around 40mA. My faulty alternator passed charging test, but with vehicle off was drawing over 500mA

 

Okay fellas an update, I went pick up my car from the Dealer yesterday after they conducted a 3rd test that morning. The alternator and battery still tested good. So I went to a different location of the O'Reilly and had them conduct the same test that the previous auto part store conducted that told me my alternator failed. He tested it and it tested good. He did state that if my car dies again, he would replace my battery because I still have a warranty on it.




I got home and let my car sit for about 3 hours. I went back out to it with my multimeter and tested 12.5 VDC without the car running. When I cranked the car, it was reading 13.57 VDC. So yes the alternator is putting out the recommended voltage. I went to my car this morning to start it and started with no problems. Guess I will just keep observing and should this happen again, have the battery changed!




Thanks for all the help guys!!! Truly appreciated!!

 

This is uncanny because the almost exact thing happened to my 2014 IS350. After 4 short trips around town (all less than 2 miles) my battery died on me Monday, wouldn't turn just rapid clicks from the starter. Jump started my car and drove it for an hour on the highway to recharge. After dinner with car off, the battery (replaced septermber last year by the dealer) is reading 12.78V. Starts it up again, at idle the battery voltage is reading 13.47V. Is that too low? Online search shows voltage when car is running should be over 14V.

After another 45 min drive home, with the car off battery reading 12.67V. 2 days later I tested the car (without any driving in between), it is reading 12.66V this morning.

Why did my battery die? My daily commute is about 2 X 15min highway without traffic. I thought that would be enough to recharge the battery. Should 4 cold starts + short trip kill the battery like that? Since I replaced the battery last year and it looking like it is holding charge ok, I suspect my alternator is going bad and not charging the battery quick enough to sustain charge.

What should I do to further test the alternator? Any help or advice would be appreciated.

 

I thought forsure this would result in a bad cell. I would bring to a battery specialist shop if you have one near. It's not a terribly difficult thing to test each cell.

As for the alternator Evey car ive ever owned put out +14v. I have read though that 13+ is normal for some.

Haven't tested the IS yet though.

 

usually healthy alternators put out ~14.2

 

Load up the alternator and see what the output is.
And load up, I mean turn every possible electrical accessory on...

• All running lights and high beam
• Hazards
• Wipers
• All dome/map lights
• Step on the brake
• Turn the radio on
• Leave the doors open
• A/C on with fan speed on high
• Seat heaters
• Steering wheel heater
• Open trunk
• Plug something into the USB's to charge
• Anything else I may have missed

If the alternator voltage output drops below 13V, then it can't keep up.
Ideally you want high 13' or low 14's.