Hello, I am new to this forum, just bought a used 1999 F-150, the battery drained and died while driving. I replace it with a new battery, then about a couple drives later it died again. I replaced the alternator charged the battery. Again after a few drives, last night I tried to start it and the battery was dead again.
what do I look at next?

 

Have you had the battery tested? Probably you just needed a new battery.

 

Just put in a New battery

 

I know you just put in a new alternator and battery. If it was a reman alternator maybe it was not operating correctly.

Go have both checked at autozone.

At this point you can get a refund if the reman alternator was bad from the start.

At least this will tell you if you need to look elsewhere or not.

 

If you have a multimeter that reads amps you can check for current drain while sitting as well.

Check battery voltage off, and running . It will be higher running due to charging from a working alternator. Around 12v off, 13+ running for example

 

Boondoggle99, your post doesn't say what engine you have. I have a '99 4.2l, and I note on Rockauto that some alternators appear to come with a new voltage regulator, but you can also buy the voltage regulator separately, at least for the 4.2. Are you certain that your reman. alt. came with a new voltage regulator? If not, I wonder if you might have a shot voltage regulator. Your symptoms seem similar to problems I have heard about where the culprit turned out to be the regulator. Good luck with it.

 

This may be a shot in the dark but if you know the alternator & regulator are good, & you know the battery is good then the only part left is the power cable from the alternator to the battery.
Could there be corrosion on the terminals or corrosion inside the cable that's insulating the conductors (copper wire) from carrying the full amps of the alternator to the battery?
IDK....just saying.

 

12v would be too low, should be 12.7-12.8v.engine off. very little difference between a dead battery and a fully charged one.

 

In my research, it looked like the voltage regulator was part of the alternator. I called O'reilly's to verify, and they said they can test it if I can drive the vehicle to them. They tested the battery, alternator, regulator and more. All good except for the battery. They said the battery registered end of life even though it was only 1 month old. I purchased the battery at Walmart, and they wanted to do their own test. It came back inconclusive, so I asked to exchange it for the maxx since it was within the 1 month store return policy. they exchanged it for me, and I am back in business, at least for now. I will give it a few days before I commit to saying the problem is fixed.
Thanks everyone for your help.
I have a 5.4 engine by the way.

 

This morning I tried to start it again with the new battery and the new alternator with new voltage regulator, and I got a click. again a click. I removed the key, and tried it again, and it started. Could it be the key switch? or starter? O'rilly's said their test showed the starter as good.