New Battery, Voltmeter Reading High All The Time

[PhilB]

About a month ago, my oem battery died when the temps were hanging below 10F. So I replaced it with a new battery from O'Reillys since theirs was an exact oem replacement. When it's cold out, you take what you can find. Anyway, took the oem out, put the new one it. Drove back to O'Reillys to get my core charge, looked at the voltmeter and the reading was right on 14. Good, I thought. Well, since I'm unemployed, I don't drive my truck everyday anymore. The truck sat for a week. I drove it last weekend and noticed that the voltmeter is reading between 14 and the next line (16?). I know that with the GMT900s, the reading will fluctuate. So I drove around a bunch, but the reading stayed above 14. Next day, I drove around some more, with the engine running for over an hour or two, and the reading was still above 14. When I got home, I got my digital voltmeter and checked the voltage with the engine running (14.7, I think), engine off(12.7), several hours later (12.6), after sitting overnight (12.4). So yesterday, I had to drive to the unemployment office which is about 20 miles away. Drove there and back home, voltmeter still reads above 14.

 

So before I take to my dealer to pay for a diagnosis, do the techs on here think it is a bad battery? Or am I having issues with my charging system? If it's a bad battery, I'll take it back to O'Reillys.

[Jsdirt]

Looks normal to me ... unless it's a conventional battery (with removable tops for adding electrolyte) ... in that case it would be on the low side at 12.4V. But my factory battery is always at 12.4 at rest.

 

I also had battery issues when I first got the truck. Always thought the truck turned over slowly. One day I ran the radio for 8 hours in the garage while my brother & I installed all the aftermarket accessories it now has. Truck had 2,200 miles on it at the time. I remembered reading that it would automatically shut the radio down in the event of low voltage, allowing you enough to get the truck started. WRONG. Just enough to click the solenoid ... and radio didn't miss a beat. Maybe I was thinking of another application ...

 

I hooked up a 3-stage desulphating charger every night for about a week, & I haven't had a problem since -- currently at close to 37,000 miles. I ran into this exact problem when working in a motorcycle dealer -- techs rushing through battery prep, resulting in a severely shortened lifespan. For the last 10 years, anytime I buy a new battery, the first thing I do is put it on the desulphating charger for at least a week. I have an 11 year old Sears Diehard out in the barn right now with 12.6V. Needless to say, that practice works.

[thearborbarber]

14.7 with the engine on is normal and your reading with the engine are spot on.

[PhilB]

Thanks for the replies guys.

 

I guess I'm more concerned with why my voltmeter in the dash is reading so high now. The needle would be about halfway between the 14 and the next line. Not right on 14 like normal.

 

I went out this morning and disconnected the + cable from the battery and left it disconnected for around 15 minutes. Kind of a reboot for the computers. Reconnected the cable and made sure both + and - are on tight. Started the truck and the reading on the gauge is now on the 14 side of about halfway to the dash. So I took the truck for a little drive. Gauge is still reading on the 14+ side. Better but I'll have to keep my eye on it. I'll drive it around some more and see if it continues to stay high or act normal. I wouldn't be surprised if the new battery were faulty. I have a 2 yr free replacement on it.

[Nytemare]

Thanks for the replies guys.

 

I guess I'm more concerned with why my voltmeter in the dash is reading so high now. The needle would be about halfway between the 14 and the next line. Not right on 14 like normal.

 

I went out this morning and disconnected the + cable from the battery and left it disconnected for around 15 minutes. Kind of a reboot for the computers. Reconnected the cable and made sure both + and - are on tight. Started the truck and the reading on the gauge is now on the 14 side of about halfway to the dash. So I took the truck for a little drive. Gauge is still reading on the 14+ side. Better but I'll have to keep my eye on it. I'll drive it around some more and see if it continues to stay high or act normal. I wouldn't be surprised if the new battery were faulty. I have a 2 yr free replacement on it.

Nope...a good new battery should read 14.2-15V...anything over 15 is bad..but if your relying on your dash gauge to give an accurate reading....thats not a great idea. your lucky if it's accuracy in within 10%...

 

Your fine.

[minibike132]

Thanks for the replies guys.

 

I guess I'm more concerned with why my voltmeter in the dash is reading so high now. The needle would be about halfway between the 14 and the next line. Not right on 14 like normal.

 

I went out this morning and disconnected the + cable from the battery and left it disconnected for around 15 minutes. Kind of a reboot for the computers. Reconnected the cable and made sure both + and - are on tight. Started the truck and the reading on the gauge is now on the 14 side of about halfway to the dash. So I took the truck for a little drive. Gauge is still reading on the 14+ side. Better but I'll have to keep my eye on it. I'll drive it around some more and see if it continues to stay high or act normal. I wouldn't be surprised if the new battery were faulty. I have a 2 yr free replacement on it.

Nope...a good new battery should read 14.2-15V...anything over 15 is bad..but if your relying on your dash gauge to give an accurate reading....thats not a great idea. your lucky if it's accuracy in within 10%...

 

Your fine.

 

 

+1

[PhilB]

Ok - so today I had to do a 50 mile roundtrip on the interstate. On the way home I stopped at O'Reillys. They checked the battery and said that it was at 84% charge. They checked the battery and said it was good. So it looks like a trip to the dealer to get this diagnosed.

[minibike132]

(Megaphone on for the cheap seats) IT'S NORMAL!!!!!! (megaphone off)

[PhilB]

(Megaphone on for the cheap seats) IT'S NORMAL!!!!!! (megaphone off)

 

Ok Sparky - so you say it's normal. How about explaining it to me how it is normal for it to run constantly in overcharge mode for 2 weeks? Are you telling me that for the last 2 1/2 years it has been running in abnormal mode because it the gauge was not reading in overcharge mode constantly? I'm not saying your wrong, but I don't know you from Adam, and just because you like to use a megaphone doesn't make you right without any proof. That would be like you asking your doctor about a mole you found on your body is cancerous, and several people in the drs office says "IT'S NORMAL". Might be but you would like some proof, wouldn't you? Again, I'm not saying your wrong. I am just asking for proof on why something that never happened before is considered NORMAL.

[thearborbarber]

Scroll down to "Charge and Discharge"

 

Then second paragraph.

 

http://en.wikipedia.org/wiki/Car_battery

[Nick The Great]

Those numbers are in line with mine.

 

I'm no battery-ologist, but couldn't a different battery read slightly different? Even 2 AC-Delco's wouldn't be exactly the same . . .

[PhilB]

Just got back from the dealer. I had called them and talked to the service advisor about my situation. They said that it was NOT NORMAL for the gauge to read in overcharge mode for that long of a period. I took it in today. They checked it all out. Battery good. Alternator and regulator good. But still in overcharge mode. They ended up reflashing the computer (BCM I think) and that seems to have corrected the issue. All I know is that driving home, the voltmeter gauge read either on the 14 or lower (for economy mode).

 

They also gave me a printout about the Electrical Power Management (EPM) which is the process GM put in with the GMT900 trucks. I have included a copy of that document for your reading pleasure.

 

I know how lead acid batteries charge from gas engines. I have two boats (5 batteries total) and I have to make sure those batteries are always healthy. I have two chargers that will desulphate those batteries also installed on the boats. I have done my research and am asking this question on this forum ("Ask the GM Tech) hoping for a tech-type answer about my situation as it relates to GMs over-charge process.

 

So I give my thanks to everyone that contributed positively to this thread.

GM_electical_power_mgt.pdf

GM_electical_power_mgt.pdf

GM_electical_power_mgt.pdf

GM_electical_power_mgt.pdf

[Nytemare]

(Megaphone on for the cheap seats) IT'S NORMAL!!!!!! (megaphone off)

 

Ok Sparky - so you say it's normal. How about explaining it to me how it is normal for it to run constantly in overcharge mode for 2 weeks? Are you telling me that for the last 2 1/2 years it has been running in abnormal mode because it the gauge was not reading in overcharge mode constantly? I'm not saying your wrong, but I don't know you from Adam, and just because you like to use a megaphone doesn't make you right without any proof. That would be like you asking your doctor about a mole you found on your body is cancerous, and several people in the drs office says "IT'S NORMAL". Might be but you would like some proof, wouldn't you? Again, I'm not saying your wrong. I am just asking for proof on why something that never happened before is considered NORMAL.

 

He's a GM tech...if he says its normal...it probably is normal...and 14.2-15V is normal...Don't you think that you would have boiled your battery dry by now if it was REALLY overcharging for 2 weeks.

And like the guys said....no two batteries are the same.

The reflash probably recalibrated the gauge....

[PhilB]

He's a GM tech...if he says its normal...it probably is normal...and 14.2-15V is normal...Don't you think that you would have boiled your battery dry by now if it was REALLY overcharging for 2 weeks.

And like the guys said....no two batteries are the same.

The reflash probably recalibrated the gauge....

In my defense, I didn't know Sparkstech is a GM Tech. Nothing in his sig or profile states that. Plus I would not have expected a GM Tech, who in a capacity of answering as a GM Tech, would respond in such a sarcastic manner. If he is answering as a GM Tech, then his actions/responses reflect upon GM and all other GM Techs in general. If he had responded in a more professional manner, and not sarcastically, then I would have taken his answer differently. I came to this forum for advice, not to be talked down to and his response just irked me a little too much that day. The company I used to work for, before I was layed off, informed all employees that if and when you are acting as a representitive of the company, on and off work, to conduct ourselves in a professional and courteous manner since our actions reflect upon the company as well as all of the other employees.

 

So maybe as a way to clarify who is a GM Tech and who isn't, those who want to help others as a GM Tech should identify themselves as such. It might help to prevent any misunderstandings.

[Nytemare]

He's a GM tech...if he says its normal...it probably is normal...and 14.2-15V is normal...Don't you think that you would have boiled your battery dry by now if it was REALLY overcharging for 2 weeks.

And like the guys said....no two batteries are the same.

The reflash probably recalibrated the gauge....

In my defense, I didn't know Sparkstech is a GM Tech. Nothing in his sig or profile states that. Plus I would not have expected a GM Tech, who in a capacity of answering as a GM Tech, would respond in such a sarcastic manner. If he is answering as a GM Tech, then his actions/responses reflect upon GM and all other GM Techs in general. If he had responded in a more professional manner, and not sarcastically, then I would have taken his answer differently. I came to this forum for advice, not to be talked down to and his response just irked me a little too much that day. The company I used to work for, before I was layed off, informed all employees that if and when you are acting as a representitive of the company, on and off work, to conduct ourselves in a professional and courteous manner since our actions reflect upon the company as well as all of the other employees.

 

So maybe as a way to clarify who is a GM Tech and who isn't, those who want to help others as a GM Tech should identify themselves as such. It might help to prevent any misunderstandings.

 

Not trying to start anything here....but....

Really...you think anyone would have responded differently to you after you were told a dozen times that it was likely normal. Sparkey knows his shit man...all you have to do is hang around these pages a little and you'll quickly realize this. Unfortunately....like most of us that know a little more than average about vehicles...he gets a little antsy when a person keeps writing back "are you sure"?...."are you really really sure"?...."well I think it may be this"...only issue with sparky over me...I learned my shit over the years...he has papers and went to school for that shit man.

 

You did what everyone should do after they get advice on here, if your unsure...get it checked. If someone here were to see your vehicle and hear the whines groans, spiked meter issues...etc...the answer may be totally different....but we go by what you are saying is the symptom...its like calling a doc and getting him to diagnose you over the phone for your illness....but you are not telling him about your explosive diarrhea...he can only diagnose what he thinks may cause your issue, on the info he has.

 

In your case...the meter read between 14 and???? the next line.

You metered the battery with a multimeter and it read 14.7...that is perfectly normal....that is what your truck should read when running....pretty much 100% of the time...overcharge is 15V and higher. I would say that there was a 95% chance that your meter was a little screwed up in your cluster....and besides its no more than 85% accurate anyway. The re-flash probably re-set the meter to factory specs and corrected its movement.