Batteries weak or alternator issue?

Easy to check your alternator.
Start the truck and Disconnect the negative on your batteries. If your truck dies the alternator isn't working.

The description you give seems the batteries are losing their charge. Disconnect the batteries from each other and test each one.

Clean all the connections.
You could have a circuit shorting out also.
Good luck

 

Alternator and batteries have a relationship. If one or both goes bad then you are stranded.

 

Id say you have a battery issue... 14 volts while running is normal alternator output.

But the discharge rate you describe when truck is turned off seems abnormally fast.

Do you have an inverter or other electronics running that could be putting that heavy of a drain on the batteries??

My gut says bad batteries... But if you dont replace bad batteries it can also kill your alternator over time, as it puts a very heavy strain on the alternator to constantly have to recharge the batteries from a low charge state.

Next time you shut down get out and feel each battery with your hand. Do this as soon as you shut the truck down... If one or more are abnormally warm, even hot, it is a sign that the batteries are going kaput.

Do you smell any sulfur smell? Like rotten eggs. This is a dead give away of a bad battery... They can even explode when they get to this point, and are almost always hot to the touch.

 

This is back yard mechanic tips, disconnecting battery to check alternator is a BIG NO-NO. The charging system and batteries can be checked quickly and accurately with a simple volt meter.

 

How old are your batteries?

It could be weak batteries or it could be a defective starter solenoid.

The slow cranking symptom can point to both of those issues.

 

If you disconnect the alternator with the truck running you will definately need an alternator. If your gauge is reading 14v when running, your alternator is fine, the batteries should be charged one at a time and then load tested to see if they are bad. If one is bad it will effect the whole group, kinda like apples.

 

Yes I am a back yard mechanic. Thanks for the information. I learned today.

 

Just because the alt is putting out 14 volts does not mean t is good, probably is, but it may not be putting out enough amps.
The battery cables are often the cause of the problem too, low voltage probably killed your last starter and it sounds as if it is working on the new one.

 

This is what I learned.
I have pulled the positive battery connection to confirm alternator has failed. Usually after voltmeter showed low volts.
This article explains what happens in newer vehicles if you use my tree shade method. As others have said.
DON'T remove battery cable to test alternator.


If it's in the range, it's good. Connect the meter leads to the battery terminals and look for 13.8 to 15.3 volts (engine running, lights and accessories off). That means the alternator is pumping out the juice.

100 Super-Simple Car Repairs You Don’t Need to Go to the Shop For

Step 2
BACHTUB DMITRII/shutterstock

If you're tempted to test an alternator by disconnecting the negative battery cable, don't do it. A good alternator may indeed keep the engine running, but it was never a good test. In the pre-computer days, you could pull it off without damaging anything. Today, you risk frying every electrical device in your vehicle. The second you disconnect the battery, the voltage regulator pegs the alternator to put out maximum power. With no battery in the circuit to act as a buffer, the alternator can put out up to 150 volts, depending on engine rpm. When the smoke clears, that “simple test” could end up costing you several thousand dollars for new electronics