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13.8V alternator charging voltage O.K? or do I need to replace alternator?

I was listening to the car radio while I was doing an oil change and some other stuff for about an hour. That was enough to drain the battery, so I was unable to start the car. I used a charger to charge the battery.

A few days later, I checked the voltage of the battery while the engine was running, and I got 13.8V. The other car I have, which had a new alternator put in about 30,000miles ago showed 14.2V - 14.4V, when its engine was running.

The car is 2003 Crown Victoria with about 100,000 miles.

Do I need to replace the alternator?
Is 13.8V high enough to charge the battery in most normal conditions including running high beam and rear window defroster at the same time?
Does the alternator degrade over time (with charging voltage slowly falling) until it completely fails, or does it fail like an electronics product?

I searched the web and found some saying the minimum alternator charging voltage is 14.0.

Your Crown Vic charging system voltage is regulated by the Powertrain Control Module.

So the PCM will only produce enough voltage to keep the electronics operating.

You don’t say the what the other vehicle is. So, it could have an internal regulator inside the alternator. And not regulated by the PCM.


You are fine, forget it.

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That’s fine. Some may disagree but anything over 13 means its charging the battery. I’d be replacing alternators left and right if I needed 14.

13.8 v is within the normal charging range. If you measure it right after you start the engine after the car sits overnight it might read in the 14’s, but will return to the 13.8 v range over time as the engine runs. Listening to the radio for an hour however shouldn’t discharge the battery so much that the engine won’t crank. Good idea to have the battery condition checked at your next shop visit. I expect you probably need to renew it.

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Like others have already said, your alternator would seem to be fine going by the voltage reading you got. You also have to consider other factors when checking the charging system. The engine speed at the time of the test and the condition of the battery will also effect the charging voltage.

Thank you.

That answers my question. The charging voltage was consistently 13.8v whether the car was in idle with no load, idle with a lot of load (high beam and rear defroster) and fast idle with load and no load.

If the voltage is precisely controlled by PCM, that seems possible.

You can buy one of those devices that plug in to the accessory socket for about $15. I have one in each car that I’ll plug in once in a while just to see what’s happening. Since they started eliminating volt gauges in cars now thinking people just don’t need to know it anyway.

It is also a function of temperature. In hotter weather the idle voltage would be lower. In cold weather higher.

I agree it sounds like your battery may be weak. Certainly inspect and if needed clean your connections. If not a maint . free battery check the water levels.

You can get it load tested at some auto parts stores for free…If it is 6 yrs old or older I would be willing to bet it is on its way out and ready to be replaced.