If alternater is putting ou 14v, charging batteries, but they are then dead in the morning would that be more likely a battery problem? Terminals clean. Batteries are Interstates, about 2 years old...Thx...Ron.

 

That sounds a good bit like bad batteries or a drain on them

 

What he said. Check the battery connections too. Did you recently install something that might be drawing power from the batteries after you shut the truck off?

 

Could be a diode in the alternator?

 

Is there a way to test that? I've already read that you can feel if the alternator is warmer than the engine temp in the morning. Will it still charge when the engine is running and have a bad diode? Will that show on a test down at local shop?

 

From what I have learned the diode will stick open so when the engine is off the power from the batteries will leak out. Take it to Advance Auto parts they have a tester that will see it.

Happened to me twice.

 

Yes it will still charge, you could just unhook the alternator for a night and see if the batteries stay charged, just be careful of the hot wire going to the alernator. I have no clue if the test at the parts store can tell if the regulator is bad or not.

 

A bad or shorted diode in the alternator can drain the battery because the alternator then becomes a load. The testors in the local parts store may not be able to test for that condition. You need to be able to read the reverse current on the alternator when a battery is still attached to it.
Nick

 

when you park the truck at night, Disconnect either both positives on the batteries or both negatives but make sure it is one or the other or hell disconnect both on both does not matter really as long as there is no power to the truck, now in the morning connect up the batteries and see what happens. should not take you more than a couple of minutes to do. this will isolate the batteries from the truck and if they are dead well you need new batteries.

One of my unofficial tests I performed on my truck when I was having problems with my batteries was this. I disconnected the passenger battery and turned on my lights and lightbar for a couple of minutes then started the truck on the one battery, the truck started ok good then I shut it off and reconnected the battery and went to the drivers side battery and disconnected it turned on the lights and right away noticed the lights were dim and I tried to start the truck only to get the dreaded click stutter. so I replaced the passenger battery and had no problem after that. I know someone will disagree but from what I was told a bad battery will drain a good battery down so this test should tell you if you have one bad battery or 2.

Hope it helps.

 

Will this condition drain fully charged batteries in one night?

 

Yes, has happened to me.

 

Absolutely.

 

The tester at Auto zone will test the diods. But you will need to pull it out. My Ex had the same thing last month.

 

Alright, seem the passenger side battery is bad. Put them on charger for a couple of work days. Passenger battery warm to the touch. Did the test by using only one battery at a time and passenger side wont crank her at all. Is is best to replace both or is it ok to replace the bad one only? Thx.

 

Best to replace both, the good one has been compensating for the bad one.