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

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.

No dice. Peak of 13.5V after 2 days on 2A trickle charger.

Gonna pull the alternator and have Az test it.

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.

Originally Posted by industrialfish

Pulled the alternator, but according to Az, you can't test this alternator off the car lol.

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.

You tested the battery out of the car or in the car at 13.5?

Originally Posted by industrialfish

Out of the car it's 12.87 and holding steady. Was 13.5 while running.

Need to do a load test to see what is going on inside.

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.

It's the regulator in the alt. Swap it and likely you'll be fine.

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.