About 6 months ago, I noticed my headlights dimming at idle. As my battery was over 4 years old, I replaced it with a new Sears DieHard. When they installed it, they noticed that the battery wasn't being charged at idle.

I can see this behavior on the voltage gauge. It drops at idle (around 600 RPM), but if I increase to around 1000 RPM the voltage goes back to normal. Since the voltage is fine at higher RPMs, the battery is charging most of the time and it hasn't been a problem.

However, today the voltage really dropped at idle to the point of the engine almost stalling. So I think the battery is shot. I will go ahead and replace it, but I'm wondering if I have something else wrong in the charging system.

The vehicle is a 2000 Expedition, 5.4L. Suggestions and comments welcome.

Thank you.

 

sounds like the alt. is going out. might want to get it checked out before it lets you sit.

 

Yes, I swapped in a new alternator and that was it. It's the vehicle's third alternator in 6 years. They don't build them like they used to....

BTW, a strange problem I was having with the wipers taking a long time to shut off or running intermittenly is gone now. I guess their controls are sensitive to erratic voltage in the electrical system.