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Discussion Starter #1
I've had my battery replaced once already and it looks like it's toast again. While driving around my voltage sits at around 12.1v and starting this morning it hit 11.5v. The only time the truck goes up to 13.7v is when my headlights are on. I called batteries plus, since that's who duracell forwarded me to, and I was told the specs of the battery for the diesel trucks. 12.9v being 100%, 12.3v being 50%, and 11.8 being 0%.


Those of you with diesels, what does your voltage usually sit at? Reading the upfitters guide page 68 through 73 of the electrical section the truck should never let the battery get this low. See attached second showing the charge mode.


The reason I'm posting this in the diesel section is I'm wondering if this document only refers to the gas engine, since it uses a different battery?
 

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We have a diesel. I have seen voltage on the DIC read as much as 15.2 volts and as low as 13.4 volts. When I check battery with engine off, it usually reads 12.56 volts. All over the board...go figure. We only have 300 miles on it so far & when we drove it home for the first time, I put an auto trickle charger on it overnight, just to make sure it had a full charge. I do that periodically because it tends to sit for weeks or longer during the winter. Retired & try not to drive it in the salt.
 

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The charging system on the diesel isn't different than the gas, it's a "smart" system so the DIC voltage will fluctuate depending on triggers/demand.

My battery was at 11.5v last week while dealing with gelled fuel in Chicago, I also got an OnStar alert warning me about low battery voltage. I also got an alert on the DIC warning me about low battery voltage and to start the truck. Everything was fine once the truck was running, no battery or voltage problems.

So, unless you're actually having a problem and are getting low voltage warnings or other weird system malfunctions then I wouldn't worry. It sounds like you're trying to find a problem that doesn't exist rather than trying to address a problem that is showing symptoms.

If you didn't look at the DIC voltage would you have any indication that there might be a problem? If not then switch away from the voltage screen and stop worrying.
 

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The diesels have a "smart" charging system which is one reason you might see the battery voltage unexpectedly fluctuate even when the engine is running. The alternator actually has a clutch pulley on it and is activated depending on system load and conditions. And when it's charging, it's not always charging full-rip. So, it can be normal to see non-charging voltages while the vehicle is idling, and going down the road with the engine at speed. The alternator should charge for roughly 90 seconds after starting and you should see maximum charging voltage of 14.5-14.6. All other times it's a crapshoot based on the logic programmed into the system.
 

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The charging system on the diesel isn't different than the gas, it's a "smart" system so the DIC voltage will fluctuate depending on triggers/demand.

My battery was at 11.5v last week while dealing with gelled fuel in Chicago, I also got an OnStar alert warning me about low battery voltage. I also got an alert on the DIC warning me about low battery voltage and to start the truck. Everything was fine once the truck was running, no battery or voltage problems.

So, unless you're actually having a problem and are getting low voltage warnings or other weird system malfunctions then I wouldn't worry. It sounds like you're trying to find a problem that doesn't exist rather than trying to address a problem that is showing symptoms.

If you didn't look at the DIC voltage would you have any indication that there might be a problem? If not then switch away from the voltage screen and stop worrying.

When running any accessories like a tire pump that absolutely loathe running at 11.9 to 12.2v, I have to turn my headlights on just to pump up a tire. AGM batteries life is cut super short by running them at 50% or lower constantly, and I don't want to have to buy a $200 battery every other year.
 

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When running any accessories like a tire pump that absolutely loathe running at 11.9 to 12.2v, I have to turn my headlights on just to pump up a tire. AGM batteries life is cut super short by running them at 50% or lower constantly, and I don't want to have to buy a $200 battery every other year.
Well. not sure what to tell you. It is what it is, my truck is ~2 years old with 25k miles and I have no battery problems and I've had no problem using a 12v compressor.
 
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I just had a conversation with my Optima battery Rep yesterday. He said todays new vehicles are hard on the OE batteries and that is why they came out with a new style.

They have moved to a new cell design for more performance and are getting away from the spiral cells on newer applications. The new battery is called a Pureflow and they have one recommended for the twins now.

They also made the move to only offer it in a Yellow Top Deep Cycle battery. They should fit most application in time.

I know some folks have had issues with Optima and others like me have had very good luck. I have two now in older vehicles one is 8 years old and the other is even older.

We do not see many warranties at work anymore. Most of the trouble we see are people using the wrong chargers on AGM batteries.

My luck with GM batteries on the last 4 cars has been just over the warranty till they died. It has not been good. My old Freedoms used to go no less than 10. One went 18 years. I only replaced it because I figured I was pushing it.

I expect many automakers will increase voltage soon. VW and Lincoln have already others will follow.
 

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The charging system on the diesel isn't different than the gas, it's a "smart" system so the DIC voltage will fluctuate depending on triggers/demand.

My battery was at 11.5v last week while dealing with gelled fuel in Chicago, I also got an OnStar alert warning me about low battery voltage. I also got an alert on the DIC warning me about low battery voltage and to start the truck. Everything was fine once the truck was running, no battery or voltage problems.

So, unless you're actually having a problem and are getting low voltage warnings or other weird system malfunctions then I wouldn't worry. It sounds like you're trying to find a problem that doesn't exist rather than trying to address a problem that is showing symptoms.

If you didn't look at the DIC voltage would you have any indication that there might be a problem? If not then switch away from the voltage screen and stop worrying.

I have a 2016 Diesel with 53000 mi 3 years of service on original battery. Like OP, my voltage is all over the spectrum. The cure - wait for it - don't look at the voltage page!! Problem solved.
 

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The diesels have a "smart" charging system which is one reason you might see the battery voltage unexpectedly fluctuate even when the engine is running. The alternator actually has a clutch pulley on it and is activated depending on system load and conditions. And when it's charging, it's not always charging full-rip. So, it can be normal to see non-charging voltages while the vehicle is idling, and going down the road with the engine at speed. The alternator should charge for roughly 90 seconds after starting and you should see maximum charging voltage of 14.5-14.6. All other times it's a crapshoot based on the logic programmed into the system.
Minor correction; the alternator has a sprag type clutch, a.k.a. one-way-bearing. It allows the alternator to freewheel if it's spinning faster than the motor. This really helps reduce stress on the components such as the belt, on motors that have big impulses when a cylinder fires, like a 4 cylinder diesel. It's all mechanical and doesn't actually have anything to do with the battery voltage.

The electrical output of the alternator is variable, but they control it all electronically. :)

For the record, it's not unusual for my battery voltage to be down in the lower 12.x range. But being in FL, the A/C is on 11 months of the year and the voltage picks right up to the 13.x range shortly after turning the A/C on. The only time it bothers me is when it's really hot outside (August, September) and I want the A/C on full blast and the battery is sitting in the lower 12.x volt range. It makes the A/C fan weaker, and you can tell immediately when the alternator starts working because the A/C fan gets a sudden boost.
 

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'18 diesel with 19k miles. I see 15.2V often on the DIC. Had me concerned for awhile but hasn't caused any issues or thrown any codes. Assumed it was due to the "smart" charger seeing an extra draw from my additional lights. 90% of my lighting is LED

2018 Summit ZR2
 

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The diesels have a "smart" charging system which is one reason you might see the battery voltage unexpectedly fluctuate even when the engine is running. The alternator actually has a clutch pulley on it and is activated depending on system load and conditions. And when it's charging, it's not always charging full-rip. So, it can be normal to see non-charging voltages while the vehicle is idling, and going down the road with the engine at speed. The alternator should charge for roughly 90 seconds after starting and you should see maximum charging voltage of 14.5-14.6. All other times it's a crapshoot based on the logic programmed into the system.
 

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You're right about the smart charging system. The alternator does not have a regulator in it, rather the computer decides how much the alternator will put out and the voltage based on a number of factors such as; lights on, charge level of the battery and outside temp. The other day with below 0 temps, I saw as high as 15.5 volts. In the summer with no lights and a full charge, I have seen down to 12.5 volts. The alternator does not have a clutch, maybe you were noticing the fan clutch slowing down the fan.
 

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2019 diesel. Votage reading when I flip through the selections is usually in the 14 volt range. I've never noticed a reading into the 15 volt range. I've seen it as low as in the high 12's from time to time but battery charging status and electrical loads will dictate the voltage displayed. What's missing is a amperage display both + and - measuring current. You really need to know what your electrical system and alternator is doing before determining what is a normal voltage reading.
 

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The alternator doesn’t have a clutch but a rectifier, which in a sense is the same thing
Just some clarification. The alternator has what's called a sprag clutch, which is common on diesels. To over simplify, it is for smoothing out vibrations and plays no role in voltage regulation.

A rectifier changes AC to DC and also is not used for voltage regulation.

The voltage regulator, whether a stand alone device or a function of the ECU, controls the output of the alternator by changing the excitation voltage of the field windings. More excitation voltage = more output, less voltage = less output. If the ECU wants the alternator to produce less power, it just lowers the excitation voltage. Kind of like how you can control the light in a room with a dimmer light switch. If you want more light, turn it up, and vice versa. The excitation voltage works in a similar way; the ECU or voltage regulator can turn it up and down to control how much output the alternator produces.
 
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