Battery Charging/discharge 2014 SLT

dat329 · August 19, 2014

The battery meter on the dashboard fluctuates a lot. Sometimes its at the half line (14) at others it reads a quarter full. I haven't had any problems starting it so far and the truck only has 2000 miles on it and I just got the truck 2 weeks ago.

Is my battery or alternator bad or is this normal. I don't leave anything plugged in and there should be no reason the battery is discharging while off.

If this is a problem, I'd like to take it back to the dealership asap. Thanks

Lawnmower2020 · August 19, 2014

It's a voltmeter. A voltmeter with unknown accuracy and lousy resolution, so you shouldn't read too much into it. It's entirely normal for it to read about 1/8 scale above or below 14. Nominal charging voltage for a "12V" lead-acid battery is around 13.8, but even that varies with temperature and state of charge. And to complicate matters further, the electrical system in these vehicles is "smart" in that it's aware of system loads (such as the a/c running) and can adjust both alternator excitation and engine idle RPM to compensate for the current load.

One more thing: There is a small but measurable parasitic current drain when the vehicle isn't running. As long as you start it up and run for a few miles every week, there's no problem other than some extra wear on the battery. However, if it's left standing for a few weeks, you are getting into a situation where you may have low-charge and poor starting especially in cold ambient conditions. So if your use involves weeks of not running, you should consider connecting a battery maintainer. There are some nice ones out there. I'd avoid those that look like wall-warts with alligator clips though. A good battery maintainer can keep a battery in like-new condition for over 10 years. It can also keep the battery strong enough to start your truck up smartly in -10F temperatures without a block heater.

Bottom line: If the pointer is in the vicinity of center, everything's fine.

GMCustomerService · August 19, 2014

The battery meter on the dashboard fluctuates a lot. Sometimes its at the half line (14) at others it reads a quarter full. I haven't had any problems starting it so far and the truck only has 2000 miles on it and I just got the truck 2 weeks ago.

Is my battery or alternator bad or is this normal. I don't leave anything plugged in and there should be no reason the battery is discharging while off.

If this is a problem, I'd like to take it back to the dealership asap. Thanks

Hi dat329,

Sorry to hear of your concerns with your dashboard fluctuating. I understand that you are seeking feedback from fellow forum members. I'd like the opportunity to discuss this with you and further investigate this concern. If you could please send me a PM here on the site and include your VIN and contact information, that would be great! I hope to hear from you.

Andraya

GM Customer Care

MikeNH · August 19, 2014

Well, no. It's a voltmeter, not a "charging meter" (by that I presume you mean ammeter). A voltmeter with unknown accuracy and lousy resolution, so you shouldn't read too much into it. It's entirely normal for it to read about 1/8 scale above or below 14. Nominal charging voltage for a "12V" lead-acid battery is around 13.8, but even that varies with temperature and state of charge. And to complicate matters further, the electrical system in these vehicles is "smart" in that it's aware of system loads (such as the a/c running) and can adjust both alternator excitation and engine idle RPM to compensate for the current load.

One more thing: There is a small but measurable parasitic current drain when the vehicle isn't running. As long as you start it up and run for a few miles every week, there's no problem other than some extra wear on the battery. However, if it's left standing for a few weeks, you are getting into a situation where you may have low-charge and poor starting especially in cold ambient conditions. So if your use involves weeks of not running, you should consider connecting a battery maintainer. There are some nice ones out there. I'd avoid those that look like wall-warts with alligator clips though. A good battery maintainer can keep a battery in like-new condition for over 10 years. It can also keep the battery strong enough to start your truck up smartly in -10F temperatures without a block heater.

Bottom line: If the pointer is in the vicinity of center, everything's fine.

That's not applicable on GM trucks and hasn't been for years. The voltage can drop alarmingly low for those accustomed to the old way you describe. My 2011 will read as low as maybe 10-11 volts. This is normal and is something the charging system does. It's explained in the manual.

Lawnmower2020 · August 19, 2014

That's not applicable on GM trucks and hasn't been for years. The voltage can drop alarmingly low for those accustomed to the old way you describe. My 2011 will read as low as maybe 10-11 volts. This is normal and is something the charging system does. It's explained in the manual.

Um...... Sorry, I don't believe that. If you see the 12V system dropping to 10-11V, then something is very wrong. Or you have a defective or out-of-calibration voltmeter. Or you're measuring it when the starter motor is running. If you have a good, properly-charged six-cell lead-acid battery, you will NEVER, and I mean NEVER see 11V in any phase of normal (not discharged) operation. Not possible.

Please cite the specific passage(s) in the owner's manual that indicate that 10V can be expected in normal operation. BTW, I have a 2011 too and have never seen a battery voltage lower than 12.5V, even under the most depleted of conditions. When it's running, the line voltage is always 13.5V to 13.9VDC, which is exactly where it should be.

BTW, there's nothing particularly special about the electrial systems in these vehicles. The basics of them are no different than 12V electrical systems have been for decades, except for 1) the additional features that speed up the engine etc. to maintain charge in high-drain situations, and 2) the intelligent load-shedding that occurs in detected low-charge situations. BOTH of these are designed to keep the battery charged and healthy to the extent possible. There is NOTHING here that would ever deliberately cause a discharge to 10-11V.

MikeNH · August 19, 2014

Um...... Sorry, I don't believe that. If you see the 12V system dropping to 10-11V, then something is very wrong. Or you have a defective or out-of-calibration voltmeter. Or you're measuring it when the starter motor is running. If you have a good, properly-charged six-cell lead-acid battery, you will NEVER, and I mean NEVER see 11V in any phase of normal (not discharged) operation. Not possible.

Please cite the specific passage(s) in the owner's manual that indicate that 10V can be expected in normal operation. BTW, I have a 2011 too and have never seen a battery voltage lower than 12.5V, even under the most depleted of conditions. When it's running, the line voltage is always 13.5V to 13.9VDC, which is exactly where it should be.

BTW, there's nothing particularly special about the electrial systems in these vehicles. The basics of them are no different than 12V electrical systems have been for decades, except for 1) the additional features that speed up the engine etc. to maintain charge in high-drain situations, and 2) the intelligent load-shedding that occurs in detected low-charge situations. BOTH of these are designed to keep the battery charged and healthy to the extent possible. There is NOTHING here that would ever deliberately cause a discharge to 10-11V.

Please refer to the thread that I pinned to the top of the tech forum:

http://www.gm-trucks.com/forums/topic/152664-2013-sierra-running-at-125-volts/

The post is about a 2013 but the new trucks have the same system. If you don't believe me, pull the plastic wrap off your manual and read it.

dat329 · August 20, 2014

Thanks for all the responses. lol, I do have to open the plastic to read the manual. I skimmed the manual online, but I guess I skimmed too much. This is the first GM vehicle I've owned. Thanks again for saving me a trip to the dealership.

gone_fishing · August 20, 2014

I just wanted to add that the gauge does appear to be pretty accurate. When I have had my ScanGauge hooked up, the voltage it reads from the OBDII port is the same as what the gauge reads. The engine temp gauge is another story.

I have noticed the voltage can drop quite a bit if there is no high electrical load such as headlights or HVAC fan at full speed. Also when its cold out, the voltage will be on the higher side (especially just after startup when I assume the battery needs a charge).

Lawnmower2020 · August 20, 2014

Please refer to the thread that I pinned to the top of the tech forum:

http://www.gm-trucks.com/forums/topic/152664-2013-sierra-running-at-125-volts/

The post is about a 2013 but the new trucks have the same system. If you don't believe me, pull the plastic wrap off your manual and read it.

Okay, so you can't provide the specific reference in the owner's manual. Didn't think so because there is no such thing. Not in my manual, anyway. And maybe you ought to READ YOUR OWN POST. The trenchant part:

The BCM will enter Charge Mode whenever [at least] one of the following conditions are (sic)

met.

....... [various conditions]
System voltage was determined to be below 12.56 V

There you have it. There's the floor to the system voltage. The engine speed and alternator excitation duty cycle will be adjusted to maintain this as an absolute minimum. A bit further down, it describes issuing a warning message at system voltage of 11V or less. So where in blazes do you get that 10V-11V is ever construed as a normal condition?

Back to the OP, there's absolutely nothing wrong with a reading such as was pictured in the referenced post with the pointer about 1/8 scale below nominal. All that says is that the battery is in good, charged condition and the charging system is coping with all the present loads. That's just where you want to see it. It's equally okay for the pointer to swing to the other side by about the same amount when the system is more heavily loaded (high beams on, rear defroster, high blower speed, etc.) and it detects that the battery isn't fully charged.

So one more time... Show us exactly where something official says that a voltage of 10V-11V can be expected in normal operation.

MikeNH · August 20, 2014

Dude, I'm right. You're wrong. If you haven't received your truck yet then download the damn manual from the Chevy or GMC fight. I'm not arguing about this anymore. It's in the manual and the person who posted in that thread, Govtech is an experienced technician.

00Silverado4x4 · August 20, 2014

Okay, so you can't provide the specific reference in the owner's manual. Didn't think so because there is no such thing. Not in my manual, anyway.

For 2006:

http://www.silveradosierra.com/download/gmc/sierra/owners_manual/2006_gmc_sierra_owners.pdf

Pg. 3-40 & 3-41

For 2014:

http://www.gmc.com/content/dam/GMC/global/master/nscwebsite/en/home/Owners/Manuals/01_Images/2014-sierra-1500-owners-manual.pdf

Pg 5-16 & 5-17

Specific enough? These pages show for both my generation and yours...2014 Owners manual.

MikeNH is not wrong! Voltage will vary as per the manuals that I have sited from GM.

Lawnmower2020 · August 21, 2014

Specifc enough? WHAT are you talking about? Where does it say there that 10-11V is within normal range? There's not a single word where you referenced that specifies any given voltage. All that says on 3-40,41 and 5-16,17 is it may read above or below center which is what I've BEEN SAYING ALL ALONG. I already quoted the applicable part from the technical reference that 12.65 is the voltage floor for 2011& later at or below which the system is forced into charge mode. What more do you want?

Show everyone *exactly* where it says that voltages of 10v-11V can be expected in normal operation. Neither of your references say that. Nothing in the 2011 or 2014 owner's manual does.

BTW, I'm not wrong. 10V on a "12V" lead acid battery is a highly anomalous condition. It couldn't occur except in cases of failed battery, deep discharge, and/or very low temperatures. It's never going to happen in any normal operational state.

So show us where 10v-11V is normal. Actual numbers, not vague descriptions. I'm not arguing about it either because neither of you guys has a documented leg to stand on. And by the way, any conclusions you're drawing from that voltmeter in the instrument cluster don't count. There's absolutely no reason to think that thing is accurate. Frankly, it's only slightly more useful than an idiot light. For that matter, you don't even know WHERE they're reading the voltage. It wouldn't be too surprising to find that voltage readings vary by a half-volt higher or lower depending on nothing more than where you measure it. Thus, the only readings I'm going to buy are from a reputable calibrated voltmeter on the battery.

And once again, there is no fundamental difference in these electrical systems compared to those of 30 years ago, except for 1) the additional intelligence built-in to compensate for load conditions by interaction with the engine control, 2) some limited ability to impute degraded battery condition by current and voltage characteristics, and 3) the ability to shed/reduce loads when necessary. Put together, all of these conspire to maintain a higher battery charge state than you'd typically expect in 30 year old designs in similar use models.

I suspect that one of the motivations for all this extra complexity in the electrical system centers on the need for a reliable and robust power supply for the electrical-assist power steering. I have some experience with BMW which has included similar features in their latest 500cc/cyl turbo platforms that also have electrical steering assist.

bdbake01 · August 21, 2014

For 2006:

http://www.silveradosierra.com/download/gmc/sierra/owners_manual/2006_gmc_sierra_owners.pdf

Pg. 3-40 & 3-41

For 2014:

http://www.gmc.com/content/dam/GMC/global/master/nscwebsite/en/home/Owners/Manuals/01_Images/2014-sierra-1500-owners-manual.pdf

Pg 5-16 & 5-17

Specific enough? These pages show for both my generation and yours...2014 Owners manual.

MikeNH is not wrong! Voltage will vary as per the manuals that I have sited from GM.

Gonna have to disagree with you here. The lawn care dude is right on. Except for possible the engine idle part, not aware of our trucks having the ability to rev up to increase voltage. However, the manual only discusses "normal range" which most certainly is NOT 10~11 volts. Normal is designated by the middle range thing on the gauge which is more representative of 12.8~14.4. Yes, I know this isn't symmetrical but hey, I didn't program it. The manual does address readings outside of this during heavy loads at idle, but it is NOT normal and must be corrected by user action.

Voltage will vary, as it should and is designed to do, but not 10V. BTW, my gauge doesn't have a "10" mark, so where you figure that is?

What I can tell you is that battery chemistry is battery chemistry regardless of where said battery resides. A 6 cell lead/lead alloy/acid battery is seriously comprised if not destroyed at 10V. You MAY get lucky and recover from 11V for a short time, but you've definitely sucked some life out of it.

To the OP, your truck is fine.