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Brand new battery not charging past 13.3V, bad alternator?

industrialfish

industrialfish

New member
Car wouldn't start after sitting for 9 days, jumped it and the voltage was low, like in the 12s. After work the battery was at 11.3 but it started. Cheap AZ battery was 5 years old so I got a brand new one, but my voltage never goes past 13.3V now.

Yes I know the 04+ only "charge on demand" but I recall it rarely being in the 13s and almost always in the 15s at night with the headlights etc going.

I checked the battery frame ground, it's good. Does the alternator just ground through it's case with the brace that goes to the engine?

Anything else I should check before buying a new alternator?
 


what are you testing the charging voltage with? 13 v is still charging. turn the head lights on, see how much it drops if at all. my cars always mid 13's.
 
DIC, Aeroforce, and multimeter all read within .1V

The 04+ have some funny deal going on where the alternator only charges based on total current draw or something, and 15V is perfectly normally during charging.

With the headlights, heated seats, and bass on, it'll drop into the 12s with the brand new battery but never higher than mid 13s, typically 13.3.

Trying to see if anyone knows of any typical issues like maybe bad alternator ground or something.
 
Here's the thing with your brand new battery, that's the only thing that you changed before this occurred. Always question the last part you put on the car if it's related.

A new battery isn't charged up when you buy it. I drained my boat battery (usually 15ish like yours) by mistake this past summer. It was a new battery and I charged it up with the car enough to get it running. Ran the boat for 45 minutes at 5000 rpm (5500 is usable redline) and then later in the day did the same on the return trip. Used no power otherwise and the battery voltage wouldn't go above 12-13 volts. Took it home and put it on an overnight trickle charge. After that it was right back where it should have been. My suggestion to you is to charge the battery overnight on a 2 amp or so charge. See how the voltage is after that.
 
That sounds like a plan. It's not my daily driver so I'll hook it up before I goto work tonight, and leave it till tomorrow.
 


Pulled the alternator, but according to Az, you can't test this alternator off the car lol. It's also a Bosch , not ACDelco, so might even be a reman already.
 
industrialfish said:
Pulled the alternator, but according to Az, you can't test this alternator off the car lol.
Click to expand...
That's funny. From their site..... Don't buy a part you don't need. AutoZone will test your car's parts for free. We can test your car's battery*, alternator*, starter* and voltage regulator while they're still on your car. We can also give your car a complete starting and charging systems test. You can also take your alternator, starter or battery into our store and we'll test it. In most stores, we can also test voltage regulators, control modules, coils, throttle position sensors (TPSs) and other engine management components.
 
I'm not sure how they would test them on the car other than with a meter anyway. They can't exactly load test them on a running car, can they? I told the guy I checked it with a meter at 13.3-13.5 and he said that alternator should be 14 minimum per the rating plate.

He didn't have any in stock, but I found one near where I work. I took an early lunch and bought it anyway. It spins WAY smoother. We'll see after work if it works.
 


Well, everything is borked now. It's going as high as 14.7 now at idle with new alternator. Except the lights are pulsing and if I give it gas it drops in the low 11s.

The belt is lined up properly, maybe it's going bad and slipping, maybe tensioner is bad. No idea now.
 
my 03 gmc i had. dic said not charging or some crap, and the batterys were wearing down, i had two batterys, so its not them, tested the alt, its weak, replace it, now im up to 14+ volts and the dic is saying over charging, took 2 more alts to get one that charged high 13's and made the truck happy. all warrany alts, same brand.
 
There is one more in stock, so I'm going to have them swap them since I'm guessing getting a refund isn't going to happen. I should have just bought a new one on Rockauto.
 


I also had a bad ground on the frame right below the battery. I cleaned it (dremel) when I installed the new negative battery cable but still had crazy voltage fluctuations and weird electrical gremlins. I ran another ground from the alt bracket to a strut bolt on the tower. Cleared it right up. Took me a long time to figure that one out. I also ran another positive from the alternator to the fuse box post to ensure a good connection.
 
You can see the weather went to crap, so I haven't been outside today. I already have a short length of 4ga from alternator directly to fuse box. The battery to body ground is good, but I didn't think about the ground on the transmission. Another engine to body ground probably wouldn't hurt.
 
2nd alternator is putting out 13.8 at idle, and also with lights, heat, and heated seats on. Doesn't fluctuate at all unless some serious bass is playing.

I'd like to see a little higher than that for the fuel pumps sake, but I guess I'll take it.
 
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