Voltage gauge normal reading

nitroduck · March 17, 2014

My voltage gauge typically reads a little over 14 volts (14.7) which is what I would expect. The other day I noticed it dropping down to a little over 13 volts. I verified with my Fluke and sure enough 13.5 volts. Is this normal on these trucks? It's usually >14 volts but for some reason I'm seeing it drop down at times.

2016 Sierra Owner · March 17, 2014

Yes just like the previous gen trucks. The volts will read between 9 and 14 depending on the load. It automatically adjusts. If you look at the gauge there is top dead center line then a line to the left and right of that. I will operate anywhere in between those in normal operation.

bdbake01 · March 17, 2014

9 is an issue, but >12.8 is just fine. In fact, the truck will actively change the voltage level depending on load/accessories inservice.

nitroduck · March 17, 2014

ok thanks for this information....real gauges!!!

jenga · March 17, 2014

I have been so used to older cars showing around 14 volts that I got spooked when it warmed up and showed around 13 volts on the way home last week. Nice to know.

michaeldc46 · March 18, 2014

Voltage will drop when the battery is fully charged and few accessories are being used - will go back to 14.7 or so to charge the battery. Will tend to drop on longer trips and go back up after a while. I assume there is a reverse current relay to ding the DIC if there is a charging problem.

nvrnuf4me · March 18, 2014

It would appear that this has been answered, but I wanted to advise what I was told by my service department.

The 2014's have a relay on the alternator that will "shut off" the alternator when the battery is fully charged allowing the pulley to spin freely similar to that of the AC clutch. When the battery charge hits a predetermined charge level due to discharge, then the relay will "turn on" the alternator to recharge the battery.

This was done in order for these trucks to be more efficient in the fuel arena.

Although, you do have to ask yourself that if the battery is constantly being discharged / recharged, wouldn't that shorten the life of the battery? Especially if it is not a deep cycle.

Hootbro · March 18, 2014

It would appear that this has been answered, but I wanted to advise what I was told by my service department.

The 2014's have a relay on the alternator that will "shut off" the alternator when the battery is fully charged allowing the pulley to spin freely similar to that of the AC clutch. When the battery charge hits a predetermined charge level due to discharge, then the relay will "turn on" the alternator to recharge the battery.

This was done in order for these trucks to be more efficient in the fuel arena.

Although, you do have to ask yourself that if the battery is constantly being discharged / recharged, wouldn't that shorten the life of the battery? Especially if it is not a deep cycle.

Unless something is new with these Alternators, it is a voltage regulator circuitry that adjusts the voltage output up and down as needed and is not a physical on/off relay. I think your dealer either did not know and/or was trying to simplify an explanation to you albeit incorrectly.

MikeNH · March 18, 2014

This is nothing new. The last generation did it to. Your owners manual (that booklet still in plastic wrap ) outlines the operation.

bdbake01 · March 18, 2014

Unless something is new with these Alternators, it is a voltage regulator circuitry that adjusts the voltage output up and down as needed and is not a physical on/off relay. I think your dealer either did not know and/or was trying to simplify an explanation to you albeit incorrectly.

What he said. I believe there are actually 3 levels, 13.2V, 13.8V and 14.4V. And cycling between the 3 are an EXCELLENT way of handling battery charge and waaay better than the old days of cooking them at 14.4V. I'm excited to see what this will do for long term battery life. While charging/discharging sounds like a bad thing, the chemistry in the battery is the final determinator and it likes to be used. Much like the human body, batteries get old and lazy if they sit around not doing anything.

For the nerds, allow me to explain my point:

A "battery" is actually a collection of one or more "cells", each with a specific open cell, float, equalize, etc. voltage. In our case with VRLA batteries (Valve Regulated Lead Acid), we have a typical open cell voltage of 2.1V with 6 cells which results in a battery that should sit at 12.6V with zero load, fully charged. Wonderful.

However, if your alternator's voltage regulator kept the system voltage at only 12.6V, then the battery would literally never charge. Or certainly wouldn't reach full charge and would therefore become useless after a point. So, it must regulate higher during operation to provide the current for your engine and accessories AND recharge the battery. Remember, these are STARTING batteries, not intended for anything else. Yes, the occasional use for the radio sitting in a mall parking lot waiting on the wife is acceptable. Using it for your bass boat's trolling motor is NOT.

So, we must run above 12.6 to recharge the battery to recover from starting. Ok then, what? Well we have choices. If you want to quickly recharge a battery to maximum potential (desirable for a vehicle which may be started/stopped quite frequently in battery terms), then you shoot for 2.4V MAXIMUM per cell. Why? Anything more at all leads to gassing. Like, lots of hydrogen gas. That's bad for a variety of reasons. Now, normally batteries gas when recharged, part of the normal process, but our sealed VRLA batteries capture this gas and recombine it through a catalyst to turn it back into electrolite. Cool huh? But ONLY if the gassing remains below the rate at which the gas recombination can keep up with. If it exceeds that, then you literally boil off hydrogen gas and destroy the battery. This starts happening at 14.400....1V. So above 14.4V charge voltage bad long term, ok?

So you start the vehicle, it shoots to 14.4V for a period, but then what? Well, it calms down to a more battery-friendly 2.3V per cell, or 13.8V for the system. This is a long term "float" voltage which is intended to maintain the maximum battery potential for extended periods without excessive gassing. Cool, sounds great.

Next, and you may see this on a loooong trip, is 2.2V per cell, or 13.2V system. This is essentially a "run the accessories" mode and will not charge the battery to any real extent, but will run all the lights and radios, charge the cell phone, etc. Battery nice and happy.

All this is awesome since on a longer trip, the battery itself heats up in the battery compartment due to engine heat, which in turn also increases gassing UNLESS you reduce voltage. So there again, cool. Remember, gassing=battery death.

There are other things that can trigger the move up in voltage such as certain high draw accessories such as heated seats, etc. This again is an effort to force the alternator to accept the load instead of the battery. Another side benefit here, as someone mentioned, is the reduced engine load at lower voltages. It's not actually the voltage that creates the engine load, it's the current (amps). But the current goes up and down with voltage, so lower voltage = less drag on engine = better mileage.

Clear as mud I'm sure. Where's my Tylenol....

nvrnuf4me · March 18, 2014

This is nothing new. The last generation did it to. Your owners manual (that booklet still in plastic wrap ) outlines the operation.

What is this owners manual you speak of?

Besides, you truck will not as valueable if you open the owners manual

JasonAVGuy · November 25, 2015

What he said. I believe there are actually 3 levels, 13.2V, 13.8V and 14.4V. And cycling between the 3 are an EXCELLENT way of handling battery charge and waaay better than the old days of cooking them at 14.4V. I'm excited to see what this will do for long term battery life. While charging/discharging sounds like a bad thing, the chemistry in the battery is the final determinator and it likes to be used. Much like the human body, batteries get old and lazy if they sit around not doing anything.

For the nerds, allow me to explain my point:

A "battery" is actually a collection of one or more "cells", each with a specific open cell, float, equalize, etc. voltage. In our case with VRLA batteries (Valve Regulated Lead Acid), we have a typical open cell voltage of 2.1V with 6 cells which results in a battery that should sit at 12.6V with zero load, fully charged. Wonderful.

However, if your alternator's voltage regulator kept the system voltage at only 12.6V, then the battery would literally never charge. Or certainly wouldn't reach full charge and would therefore become useless after a point. So, it must regulate higher during operation to provide the current for your engine and accessories AND recharge the battery. Remember, these are STARTING batteries, not intended for anything else. Yes, the occasional use for the radio sitting in a mall parking lot waiting on the wife is acceptable. Using it for your bass boat's trolling motor is NOT.

So, we must run above 12.6 to recharge the battery to recover from starting. Ok then, what? Well we have choices. If you want to quickly recharge a battery to maximum potential (desirable for a vehicle which may be started/stopped quite frequently in battery terms), then you shoot for 2.4V MAXIMUM per cell. Why? Anything more at all leads to gassing. Like, lots of hydrogen gas. That's bad for a variety of reasons. Now, normally batteries gas when recharged, part of the normal process, but our sealed VRLA batteries capture this gas and recombine it through a catalyst to turn it back into electrolite. Cool huh? But ONLY if the gassing remains below the rate at which the gas recombination can keep up with. If it exceeds that, then you literally boil off hydrogen gas and destroy the battery. This starts happening at 14.400....1V. So above 14.4V charge voltage bad long term, ok?

So you start the vehicle, it shoots to 14.4V for a period, but then what? Well, it calms down to a more battery-friendly 2.3V per cell, or 13.8V for the system. This is a long term "float" voltage which is intended to maintain the maximum battery potential for extended periods without excessive gassing. Cool, sounds great.

Next, and you may see this on a loooong trip, is 2.2V per cell, or 13.2V system. This is essentially a "run the accessories" mode and will not charge the battery to any real extent, but will run all the lights and radios, charge the cell phone, etc. Battery nice and happy.

All this is awesome since on a longer trip, the battery itself heats up in the battery compartment due to engine heat, which in turn also increases gassing UNLESS you reduce voltage. So there again, cool. Remember, gassing=battery death.

There are other things that can trigger the move up in voltage such as certain high draw accessories such as heated seats, etc. This again is an effort to force the alternator to accept the load instead of the battery. Another side benefit here, as someone mentioned, is the reduced engine load at lower voltages. It's not actually the voltage that creates the engine load, it's the current (amps). But the current goes up and down with voltage, so lower voltage = less drag on engine = better mileage.

Clear as mud I'm sure. Where's my Tylenol....

Hey that was a great post about the battery and helped me a lot with understanding the charging system. I have added a second battery with a blue sea system isolator. My switch for the unit has a connect , disconnect, and auto mode. It lights up when the battery's are connected. So when the main battery is over 14ish Volts for over 90 seconds it kicks in then when the truck drops voltage for more then 90 seconds it disconnects. During my looking in how to connect my sistem I found out that for the truck to see the second battery my negative lead had be connected to the trucks house battery. At the moment I have not added a smaller sub lead to the frame because I'm not sure how it will affect the system. Any thoughts or advice would be great.

redwngr · November 26, 2015

Hey that was a great post about the battery and helped me a lot with understanding the charging system. I have added a second battery with a blue sea system isolator. My switch for the unit has a connect , disconnect, and auto mode. It lights up when the battery's are connected. So when the main battery is over 14ish Volts for over 90 seconds it kicks in then when the truck drops voltage for more then 90 seconds it disconnects. During my looking in how to connect my sistem I found out that for the truck to see the second battery my negative lead had be connected to the trucks house battery. At the moment I have not added a smaller sub lead to the frame because I'm not sure how it will affect the system. Any thoughts or advice would be great.

Have a look at a Duramax. They all have 2 batteries.

bdbake01 · November 26, 2015

Hey that was a great post about the battery and helped me a lot with understanding the charging system. I have added a second battery with a blue sea system isolator. My switch for the unit has a connect , disconnect, and auto mode. It lights up when the battery's are connected. So when the main battery is over 14ish Volts for over 90 seconds it kicks in then when the truck drops voltage for more then 90 seconds it disconnects. During my looking in how to connect my sistem I found out that for the truck to see the second battery my negative lead had be connected to the trucks house battery. At the moment I have not added a smaller sub lead to the frame because I'm not sure how it will affect the system. Any thoughts or advice would be great.

Thanks! Glad I could help. As for your negative lead on the secondary, where is it connected now? There's no need for it to be connected directly to your primary. However, it should have one, and ONLY one very substantial lead going directly to a GOOOOD ground point, preferably on the truck frame using the shortest route possible.

JasonAVGuy · November 26, 2015

Thanks! Glad I could help. As for your negative lead on the secondary, where is it connected now? There's no need for it to be connected directly to your primary. However, it should have one, and ONLY one very substantial lead going directly to a GOOOOD ground point, preferably on the truck frame using the shortest route possible.

Right now my main 2/0 ground is going back to the first battery I was told by GM that if it was going to the trucks frame it would bypass the voltage computer that controls the altanator. They said it was on the negative ground of the main battery lead.