If the electrical gauge on the dash shows 14.5'ish volts all the time while driving or at a stop, does that mean the alternator is producing enough Amps to keep the battery charged?

I have a vehicle (2002 Trailblazer) that I had to replace a four year old battery with a brand new battery (NAPA). Then after one month, the engine would crank fine one day and barely turn over the next day. So I checked the battery during cranking and it showed 10v. So I took it in and they load tested it and it showed 81a on a 695a battery. Cool, the battery was bad and they gave me a new one and I took it home. The car started fine for two weeks and now this morning (in the garage, 51 degrees), I turn the key and it barely turned over and then it started up. The battery was so low that the interior lights did not come on until the engine fired. The car ran great yesterday. The voltage gauge showed 14.5v as soon as it fired up and I let it idle for a few minutes and I drove it to work with no problems. The guage never moved from the 14.5 volts at any time during the 30 minute drive to work. But I am worried how it will act after setting for 12 hours before I get in it again.

I am planning on stopping by NAPA on my way home today to have them test the battery on the vehicle.
- Is there a chance that I got a second straight bad battery?
- Is there a chance that my original 2002 alternator is making 14.5 volts but not enough amps to keep the batteries alive?
- Can they test the alternator on a running car?

Thanks

voltage is a function of current, which is a function of voltage.

Can't have one without the other.

Voltage equals current times resistance.

So if voltage is right and nothing changed resistance wise then current is right.

Getting two bad batteries is entirely possible.

Thanks Super!

I will stop by NAPA to have the battery checked first. Then I will pull one of the cables off of the battery tonight too see what the amp draw is with the engine off. Maybe I have a draw bringing down the battery.

I do have another issue with the vehicle which may or may not be another issue. I have been having an issue during startup. The engine may crank for 2-3-4 seconds before firing. I have changed the fuel pressure regulator due to a full 54psi at idle. After this change, the idle is now 51psi. After I made this swap, shortly after the delayed starting issue became an issue.
I am wondering if the low battery and the delayed starting of the engine may be connected. Bad starter drawing down the battery?

Thanks again.

No way you got two bad batteries. My bet is what you have is a draw with the ignition off. Open a door and latch the door latch so the body controller thinks the door is shut (this will allow you to get inside the vehicle without waking up any modules). Disconnect one battery cable. Put a test light in between the removed cable and that bartery terminal.the light should go off after all the modules go to sleep, no more than 10-15 minutes. If it stays illuminated start pulling fuses until it goes out. Then trace that circuit.
Doug

.

We'll find out when it gets tested.

Doug,

I just copied/printed your response. I am going to put an amp gauge on the battery cable at lunch to see what the draw is after setting for 5 hours. If this shows a major draw after the interior lights are off, then I will use your notes tonight to trace down the circuit.

How much draw should I see with the engine off? Less than an amp?

I will have the battery tested on my way home. This way it will be charged up when they test it.

Thanks to everyone!

Over 50 milleamp is enough to kill it.
Doug

The vehicle sat for 5.25 hours this morning. Battery voltage showed 12.6v and the drain at the positive battery cable measured 1.2a. Then I turned it over and it barely had enough to crank while showing 10v. Then it fired up and read 14.8v over a 3 minute span.

What do these numbers tell me? Is the 1.2a drain a lot for 5+ hours?

The 10v during crank was exactly what it read when I took the last new battery in to swap it for this one.

Is the 14.8v enough out of the alternator right after a 10v crank? Should the alternator be putting out more than 14.8v to charge the low battery back up?

Thanks again!

Over 50 milleamp is enough to kill it. Google it, common issue. On Star module, lift gate module among others.
Doug

I just read a few posts showing .5a was too much of a drain, let alone 1.2a.

I will hookup my meter tonight and start pulling fuses.

Thanks!!

U have something drawing down the battery...
Such as a stuck brake lite switch.. Under hood courtesy lite..

A good electrical system including battery should be capable of handling up to a 150 milliamp draw for at least a week if things are rite...

Just my $0.02...

This^ you most likely have a draw. Actually you already proved it.

Trailblazers are an electrical nightmare, ran into one a while back where the cluster would intermittently turn on. The cluster itself was not much draw but when it wokke up it activated the radio amp.

Too much interconnected bs on new stuff anymore.

Recap:
This morning 5:45am: engine would barely turnover, but started.
This morning 11:15am: checked standing voltage at 12.6, 1.2a draw, 10v crank, 14.5 run. It would barely turn over again and I let it idle for 3 minutes or so.
5:00pm: Started just fine!!!!!!

Stopped by NAPA (15 minute drive) and they tested the battery and the alternator and both checked out very good condition. Battery was showing 875+CCA and the alternator showed 14.2 during different rpms and loads and the battery held the charge.

Tonight I found some corrosion on the positive battery terminal. This may be the starting issue due to bad connection.

I also found a blown fuse on #40 (TBC4, rear bank). While checking all fuses/relays, the amp draw was 1.6/1.7 until I pulled the #41 fuse (radio) and then it went down to .89a.

I am not sure what the TBS4 fuse (10a) goes too, but I replaced it. The radio fuse seemed to be the biggest draw at .71a.

But after pulling the radio fuse I still had .89a which seems too much.

The only "known" electrical gremlin is the heater/ac vent door motors. They click/click every time during startup or when the defroster/heater is changed back and fourth.
The only known fuse that I did not find is the one for the aftermarket sunroof. I bet it was wired with an inline fuse somewhere under the dash.




What do you guys think?

Thank you.

TBC4 is interior lights, do they, or rather did they, all work?

I replace the fuse and noticed that the rear light might be working now😀. I have been driving this vehicle every day for many years and I may have gotten used to some imperfections. But I am thinking of disconnecting those vent motors that click at me every time I tart it up.

Thanks Super.

Also remember that some electrical units (modules) can take up to 20 minutes to time out. So make sure you wait long enough to be sure everything is timed out. Ron

The problem came back this week. Sometimes it starts right up and sometimes it drags down and the lights dim. Since after pulling all of the relays and fuses one by one and the amp draw did not change (except the radio), I purchased a new starter and I plan on swapping that out this weekend. I am hoping that the 14 year old original may be the issue. I will take a reading on the amp draw before and after the swap.

Thanks everyone.

I replaced the starter yesterday and the vehicle starts in less than a second after turning the key. No more 3-4 seconds of cranking before the engine starts. No more slow cranking like the battery was dead.

I did check the amp draw before and after the starter swap and the 1.6a did not change. But the 14 year old vehicle starts like it is new.

Thank you everyone for your help.