Battery light on all the time but truck seems fine?

[fiddlermd]

Battery was around 9-10v. Wouldn't start. Boosted. After running for a couple minutes, village is 12.6 . If I crank engine, good up to 14.1. with accessories on, 11.1 and falling. Is it regulator again? Could there be a condition that's frying the regulator?

 

[fiddlermd]

went out to the car. 9v at the battery - car won't start. boosted it. after a minute, hovers around 12.6.. if i crank the engine, goes up to 14.1 or so. if i turn on accessories it goes to around 11.2 and then starts falling. is this regulator again? considering i just swapped it, is there a condition that would fry the regulator?

 

[RonD]

You have lost 1 or 2 fields in the alternator itself so no not just the regulator
This is one of the issues that can come up by just replacing the voltage regulator in an alternator and not replacing the whole alternator

Lowest voltage with engine at idle should be 13.5volts

Unhook either battery cable and test battery voltage, write it down on the top of battery
Then test voltage again after 2 to 4 hours, longer is better, i.e. over night, if voltage is lower on re-test then battery is SELF DRAINING, so has an internal short, this is caused by draining any car battery below 12volts consistently/repeatedly

Car batteries are made to start the engine, that's all, alternator powers ALL the electrics once engine is started

So you will probably need to change both alternator and battery at this time
Bad alternator can damage new battery
Bad battery can damage new alternotor

 

[fiddlermd]

interesting - thanks! any recommendation on which alternators to avoid?

 

[RonD]

Broken ones

As long as its warrantied it should be fine

 

[rubydist]

I have had the best luck with the NAPA lifetime warranty ones.

 

[RangerBilly]

I've had the battery light on for at least a month.. probably more. I did have some weird issues with cold starts but they seemed to have gone away now. In any case, truck starts, battery doesn't die. It runs ok but the low battery light is always on.
What else could it be?
Not sure if it's related, but I noticed recently that even on cold start, my engine temp gauge jumps right to the middle immediately even though obd2 reports something like 97 degrees.. guessing one of those sensors went bad?

My alternator was showing signs of giving up the ghost. I got it almost exactly a year ago -- a rebuilt Ultron from O'Reilly's. The symptoms were: battery light remained illuminated regardless of the engine speed, though sometimes it would flicker if I blipped the throttle. This had been going on for six months but the battery never got weak, and the truck always started!

Also, the system voltage at idle would drop to 12.6 if I turned on the headlights.

Thankfully it was under warranty. Took about a half hour to replace. Works fine now. Voltage is rock steady and that annoying red warning light is off.

So I'm guessing that your alternator may be having a similar problem. That low battery light is driven directly from its voltage regulator.

Don't need a dead battery tomorrow morning trying to get to work on time!

 

[fiddlermd]

Sorry for lack of follow-up. It was the alternator. I replaced it and all the issues went away. Thanks for the help!