Alternator or battery?

[Rick Boswell]

While driving the other day, suddenly my Expo tried to stall several times ABS And battery light came on together. As long as I could keep the RPMs up the voltmeter would come back up. Fortunately, I was close to home and made it on in. Next morning dead battery. The battery seems to be holding a charge after being on the charger overnight. Battery or alternator? 2003 XLT 178k.

 

[Don Hall]

Many auto stores (AutoZone is one) will load test batt and alt for free......

 

[Plati]

I have an 03XLT. It could be a lot of things, really … not just those two. BUT you need to run some diagnostic tests. How old is the battery? If its more than 3 years old just replace it anyway. I THINK if the alternator is good it will stay running as long as its running? So I'm guessing alternator. You can have the battery tested for free at a parts store.

What is the (engine not running) voltage of the battery after being FULLY charged?
Whats the voltage after sitting 2 hours?
24 hours?

Whats the voltage of the battery drop to while starting,
and after starting (running)?
Whats the voltage if you turn on the headlights (engine running)?

I've had bad alternators … marginally bad alternators, bad battery .. etc.

 

[Cooper]

Id replace both... but its atleast the alt.

 

[Plati]

Id replace both... but its atleast the alt.

I'm a big fan of finding the root cause by diagnosis. When you start removing parts and replacing them you often introduce a new problem or temporarily mask the original problem. Then later the original problem comes back. Not being critical of this suggestion, just a different take on it. It could be a broken wire or bad connection at at terminal or ???? Could just be a loose connection on the battery terminal. No guarantee a "new" alternator is good. I had a problem in my 2003XLT and put in a "new" (rebuilt) alternator. Turns out the alternator I put in was marginally bad and it replaced an alternator that was just fine.

 

[Cooper]

The exact same thing happen to my wifes 07. It was the alt and since the battery was overly wet on the caps I changed that too. Twoyears later no issue.

But I get your point of finding out root causes but, some times its just good ole parts failure.

 

[Trainmaster]

If you're one to just throw parts at the problem, be sure to check your cables first. They can get nasty and cause you many problems, the least of which is the money you'll spend replacing good stuff.