Jumped the truck for the trip to parts house for new alternator, on the way home old one must have froze up; made a terrible screeching, grinding sound and immediatley drew down the battery so the truck died within 60 seconds.

Installed new alternator, everything fine for a few weeks. Now after sitting overnight or several hours it's slow to start and gauges stay down for several seconds, connections seem OK and it's reading 14.8 to 15.1 vots across the battery while running.

Any Ideas?

 

Bad battery. Won't hold a charge. The reading while running is the altenator output.

 

Yeah, it is your battery... if it is stock it is 4-5 years old.

 

If you bought a rebuilt alternator, I'd suspect the alternator. Most rebuilders do not replaced the voltage regulator in these things. What happens is that the final diode burns out. That diode is what keeps the battery from draining back thru the alternator when the key is in the off position. You can't go by the output because it will charge the battery but drain it back out. Easiest way to check it is to make sure the battery is fully charged and disconnect the battery while it sits over night or for a couple of days. If you hook it back up and it starts like it should, it's the alternator. It it doesn't, go buy another battery.

 

14.8 is too high. Specs are 13.8 to 14.4 when running. If you keep overcharging it like that, you will kill the battery.

If you go over to Autozone, they can test the battery and alternator on the vehicle. I'd assume other parts stores can do the same. Whatever you do, don't buy an Autozone reman alternator, they are very unreliable. Their batteries aren't the greatest either, but I've got 2 over here and they are both fine.

 

I'm pretty sure the battery is good, it's only about 12 months and has shown nothing to this point. I'l try the disconnecting the cable test, it sounds like that might be the issue.

Thanks, I'll let you know what happens.

 

Turns out it was the battery. It was only 12 months old and in good shape, but the guy at A-zone tells me draining and recharging a battery seeral times in a row can ruin it. It appears he was right; at least in this case. Learn something new everyday!