Alternator questiom

[DWBOX2000]

Daughter’s car battery went dead this morning. It’s over 8 years old. AAA came and the guy said battery is toast and so is alternator. Knows a guy that can fix it. Well I drop in new battery which reads 12.5v. I start and meters reads 14.4. Should it be running higher. Seems okay. Thanks.

[rfuerst911sc]

At what RPM did you measure 14.4 ? What is the measurement at idle and then at 2k ?

[DWBOX2000]

At idle 14.11. Don’t have anyone to hit throttle and no broom sticks around.

[JackDidley]

Battery volts + 2 is pretty normal. I think AAA guy is not a mechanic.

[908/930]

How many miles on the car? I find alternator brushes usually can last to about 130k miles. At 8 years likely just battery. 14.4v sounds about correct.

[HobieMarty]

That sounds about right to me. 8 year old battery? Yeah, that lasted well beyond its lifespan.

Sent from my SM-S916U using Tapatalk

[pmax]

Originally Posted by DWBOX2000

... AAA came and the guy said battery is toast and so is alternator. Knows a guy that can fix it.
...

[DWBOX2000]

I went for a 20 minute ride, still idling at 14.10.
Car has only 65k. All seems fine but I’ll keep eye on until I go home. What does a car need in volts to run?

[908/930]

Originally Posted by DWBOX2000

I went for a 20 minute ride, still idling at 14.10.
Car has only 65k. All seems fine but I’ll keep eye on until I go home. What does a car need in volts to run?

Min is probably around 11v, so 14v is lots.

[masraum]

Battery voltage fully charged should be 12.6 (may be higher due to surface charge).

charging while running should be 13.8 and up (I'm sure there's a max, but can't remember if that's 15, 16, 18, etc...)

Battery likely dead, not alternator.

Batteries can be discharged (<12.5V) due to having something left on (lights, etc...). A discharged battery (if that's the only problem) can be charged back up and be fine.

Batteries can be "dead" not sure if there's another/better term, where they have a full 12.6V charge, but have lost the cranking amps to start the car. I've seen this 100 times, get in the car, start it and drive it and everything is fine. Stop the car, come back out to start the car and you may or may not get a click or even interior lights. Car likely showed 12.6V (until you tried to start it which may have run it down). That battery is just done, no fixing it with a charger.

That probably what you ran into. I've heard that sort of battery death is due to the coating on the plates flaking off or otherwise changing. I've heard of "internal shorts" too, but I'm not sure exactly what that is referring to.

[Scott Douglas]

What's the reading idling if you turn on the lights and a/c?

[pwd72s]

Originally Posted by 908/930

Min is probably around 11v, so 14v is lots.

14 is ideal as an alternator's output...masraum said it well. Seems to me the tow truck driver was trying to help a buddy...

[Scott Douglas]

I'd like to know what brand of battery lasted 8 years.

[908/930]

Originally Posted by pwd72s

14 is ideal as an alternator's output...masraum said it well. Seems to me the tow truck driver was trying to help a buddy...

He asked what the min voltage is for a car to run, not that it will start again when at 11v. Depending on battery type AGM vs FLA will likely change the charge voltage.

[Noah930]

Originally Posted by JackDidley

Battery volts + 2 is pretty normal. I think AAA guy is not a mechanic.

Based upon my interaction with a AAA battery guy, I would agree.

I had a AAA battery in my daily driver. It lasted 2 years. I got it replaced under warranty. The replacement battery also died in short order. In the meantime, I had already gone through the car looking for parasitic draw, etc.

So at the 2nd battery failure, I once again called AAA as the battery should still have been under warranty. He hooked his equipment up to the car (while idling) and told me the alternator wasn't working, so all he was willing to do was give me a jump start. No replacement battery.

However, like you I had also checked the car while running, and it was putting out 14+ volts at idle. So I decided to go buy a Costco battery instead as a replacement. That was about 4 years ago. Still running with the same Interstate battery from Costco. Still haven't touched the alternator.

[Noah930]

Originally Posted by Scott Douglas

I'd like to know what brand of battery lasted 8 years.

I bought a '95 Nissan, new from the dealer. The Nissan-branded battery lasted 10 years! And the car lived outdoors in New England for the 2nd half of that.

Otherwise, batteries in daily drivers seem to last me 3 years, on average. If I throw the car on a battery charger every once in awhile (like on the garaged Porsches), then maybe I can add another year or two to that.

[Noah930]

Originally Posted by masraum

That probably what you ran into. I've heard that sort of battery death is due to the coating on the plates flaking off or otherwise changing. I've heard of "internal shorts" too, but I'm not sure exactly what that is referring to.

I think (from some retired enginerd from a Ducati board?) that an internal short is when a plate sulfates, and then the plate (with the sulfate build-up) starts touching adjacent plates.

[pwd72s]

With the price of batteries today, I feel the price of one of these is more than justified...pretty much eliminates guesswork. Warning! Mustang content...may not be suitable for some on this board...risk of head explosion.

https://www.youtube.com/watch?v=b6G4zKqpp2M&ab_channel=Smackey%27sGarage

[masraum]

Originally Posted by Noah930

I bought a '95 Nissan, new from the dealer. The Nissan-branded battery lasted 10 years! And the car lived outdoors in New England for the 2nd half of that.

Otherwise, batteries in daily drivers seem to last me 3 years, on average. If I throw the car on a battery charger every once in awhile (like on the garaged Porsches), then maybe I can add another year or two to that.

My experience have been that most OEM batteries seem to last a long time, 7-10 years, but that most aftermarket batteries last 1/3 - 1/2 that long. I think there are likely some aftermarket batteries that last like OEM, but I don't think most folks splurge for the "top of the line" when they buy a new battery. AGM may last longer than FLA under the same circumstances, but I don't know that for sure.

[masraum]

Originally Posted by Noah930

I think (from some retired enginerd from a Ducati board?) that an internal short is when a plate sulfates, and then the plate (with the sulfate build-up) starts touching adjacent plates.

OK, so basically what I'd been told about the reason for the dying with more detail. Cool, thx.