2015 Duramax Charging rate?

R Q

R Q

Well-Known Member
Joined
Apr 4, 2005
Location
Charlotte
I had a bad battery so I replaced both. When the bad battery was still in the truck the volt gauge would read at about 11 then slowly (3-5 minutes) work it's way up to 14+.
Put two new batteries in and it's doing the same but is actually going close to 15 or maybe a little more. I'm not getting good info on Google searches, answers are all over the place. I'm thinking maybe the bad battery ruined the alternator? I don't want to fry my new batteries.
 
Do these cycle the glow plugs on and off after startup in cold weather? My Cummins does with the grid heater and it'll flip flop the voltage gauge from 12-14 for a few mins after start up in the cold.
 
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Chris_Keziah said:
Do these cycle the glow plugs on and off after startup in cold weather? My Cummins does with the grid heater and it'll flip flop the voltage gauche from 12-14 for a few mins after start up in the cold.
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This. I'd bet there's some sort of electric resistance element (grid heater in the heater box might also be an option) that runs on startup and pulls huge amps.
 
I put a meter on the batteries this morning at a cold start and got 10-11. It stayed pretty low and gradually started coming up. I’m thinking it’s the alternator because it didn’t get up to full charge in the few minutes we were testing it. It’s never read that low on the truck gauge and I want to verify that with the meter. I would say that my old bad battery ruined my alternator.
 
R Q said:
I put a meter on the batteries this morning at a cold start and got 10-11. It stayed pretty low and gradually started coming up. I’m thinking it’s the alternator because it didn’t get up to full charge in the few minutes we were testing it. It’s never read that low on the truck gauge and I want to verify that with the meter. I would say that my old bad battery ruined my alternator.
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Truthfully needs to be checked at the alternator to verify. Seen quite a few times a dead/low battery give a funky reading.
 
On a 15 duramax you have all kinds of EPA regulated stuffs. You have glow plugs, grid heater which both pull some huge amps. My 19 battery gauge will dip down on a cold start due to this.
 
After a lot of checking volts and letting it run a while, I decided that my new batteries may have been low from sitting on the shelf. All seemed better after running for a bit. Another cold start this morning should let me know...
 
shawn said:
This. I'd bet there's some sort of electric resistance element (grid heater in the heater box might also be an option) that runs on startup and pulls huge amps.
Click to expand...
LBZ_Duramax said:
On a 15 duramax you have all kinds of EPA regulated stuffs. You have glow plugs, grid heater which both pull some huge amps. My 19 battery gauge will dip down on a cold start due to this.
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My money is on this. The voltage on my 7.3l stays low for the first couple of minutes while the glow plugs are on and then the voltage starts creeping up after they turn off.
 
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