Battery or alternator?

Have a 2006 Ford Focus 150 HP. All of a sudden the battery goes dead. Charge it and it’s okay and then after a few days you turn the headlights on and the radio just dims right off.

Took it to the Ford garage and they said the battery was fine. Have 50,000 well cared for miles on it.

Any suggestions? I know there was a Ford service bulletin on the 2004 Focus alternator.

Since you use the word “dims,” I think you’re correct in suspecting the alternator. You can drive on the battery alone, and your accessories will go out and the lights will dim slowly as the current is slowly drained. If this happens suddenly and all at once, then it’s a different matter. Can you drive for longer without the headlights on? That’s a good indication that your alternator is not putting out.

AutoZone and some other auto parts houses test alternators for free. If you’re driving along and it starts to die slowly, turn off all of your accessories (radio, air, etc.) then find the nearest parts house and have them check the alternator before the car quits running. I’m thinking you’re right.

When alternators fail, there is usually a dashboard warning light…Is your car equipped with a voltmeter so you can monitor voltage? If the battery and alternator check out, then you have a parasitic load draining the battery. That too is easy to find. Time to find a good independent mechanic. The dealership people just don’t care…

The reserve capacity of a battery is how long it can take a 25 amp drain (without a functioning alternator) before discharging below 10.5 volts.

If you have a 120 minute reserve capacity, that’s a ballpark of about how long you’ll run your car before the battery goes dead on you without an alternator.