Battery / alternator issue

[Jones]

I wanted to get some insight on this. I just replaced my alternator as I had just replaced my PCM because the voltage indicator on the dash would die while driving. I replaced the alternator a few days ago and the voltage on the dash is fine now. But I’ll turn the Jeep off and go to turn it on and it doesn’t crank. I have to get jump starts off my old lady to get it to crank. I tested the voltage on the battery with a voltage tester and got the regular numbers 12,13 so on. And also tested the alternator which gave me 13.8 which I believe is normal. I thought the alternator was faulty but I got it to crank earlier after jumping it off and then removed the negative from the battery terminal and the Jeep ran fine still. Reconnected, turned it off, *click* nothing. I got a new battery in early summer 2019.

Insight here? Could the battery still be bad even though it’s reading good voltage? Would replacing it fix this issue? Thanks!

 

[Chris]

How old is the battery, what is the date on it?

The battery voltage means nothing without load testing it. Have you load tested it?

What kind of condition are the battery terminals in?

 

[Jerry Bransford]

Don't measure the voltage on the battery with no exceptional current draw on it, even a nearly dead battery can measure 12 volts. Instead, have a helper turn the ignition switch to Start and you measure its voltage on the battery post, not its connector, while the ignition is in the Start position.

If the voltage at the battery post drops off when the switch in in the Start position, the battery is the problem. Maybe it just needs a good charge, maybe it's going bad prematurely. If the voltage on the battery post itself stays at 12 volts while the ignition switch is in the Start position, move the probe to the battery connection and see if you are seeing the same 12 volts. If it drops off on the connector, wire brush the battery post/inside of the connector and try again.

If all that's ok, time to move to the starter solenoid and the wiring between the battery and starter, and the wiring between the starter solenoid and the starter relay inside the Power Distribution Center.

 

[Zorba]

What Jerry said. I'll only add that if you drained the battery flat while you were dealing with your alternator situation, that could have killed it (the battery) then.