Alternator need replacing?

[Michigan]

So my 2004 z71 has had a string of electrical problems

January 1st this year I had a new battery replaced under warranty as I had it in a few shops for parasitic draw

The new battery did drop to about 2 volts but recharged it and a shop had told me that I had a parasitic draw coming from my instrument cluster, I had the cluster sent out and rebuilt

After the cluster rebuild, I noticed that if I don’t drive the car for a couple days that it gets down to about 12.0 volts and that I seen that’s about 75 percent or so but a mechanic told me not to worry about that

Today I was at the auto parts store for something else and mentioned to the guy that it gets to about 12.0 or even 11.9 volts after a few days and he ran a test and said that I need to change the alternator and battery

Truck has been starting up fine.

I thought all was finally well until the test

Thoughts? Do I need to or should I change both? They said they’ll change battery under warranty if I buy the alternator from them which is about $210 plus labor

 

[Doubeleive]

tough one, I guess it depends on labor and if the alternator is oem and/or has a lifetime warranty.
if you buy the alternator and diy and still get a new battery out of it then that's a plus
changing the alternator is fairly easy with basic tools.
the starting voltage looks fine, 10.5v is the "rule" on that.

 

[Fless]

Moved you here from the 2007-14 section.

When you get the battery load tested they should give you the printout of the measured capacity. Get the details for an informed decision.

 

[rockola1971]

Your automotive parts guy is just that....not a mechanic. How exactly does he know that the alternator and battery are bad without even testing them? Ignore that fool. More than likely your problem is the BCM not going to sleep causing the parasitic draw. The cause is usually a corroded, broken or loose ground which gives the BCM a ground reference. Check the grounds at the drivers side frame rail just below the firewall AND also the ground that connects the rear of the engine block to the firewall. Ive even heard of a ground in the A pillar causing havoc too. It isnt unheard of to have alternator's diode pack having a leaky diode load down the battery when vehicle is shut off.