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What is normal battery voltage?

98K views 12 replies 8 participants last post by  Johnp3 
#1 ·
I'm curious if my batt voltage is considered normal or little low.
11.6 cold start glow plugs on, 12.7 KOEO after running, 14.2 running voltage (Alt charging)

I have a pair of 850 CCA.
 
#2 ·
Thats what mine reads off of my ScanGauge2 mounted inside the cab, exactly the same numbers as yours.

Harry
 
#3 ·
Great, I feel much better now!
 
#4 ·
Ditto what Harry said. Nothing out of the ordinary with your numbers.
 
#5 ·
Slightly off topic, but my running voltage is typically 13.6 down to 13.2. My gauge is a DMM (digital multimeter). I've never had mine run at 14V for any length of time.

Does the alternator/charging logic adjust the running voltage if the batteries don't need charged much? Or should it *always* be 14V? Mine will start higher, then drop down as time moves on. When I plug in my trailer, It runs closer to 13.2 for most of the haul. All the batteries are charged before trips.

Thanks.
 
#6 ·
A battery needs 13.8 volts to charge.
What I do to test a battery, is after sitting overnight, it should have 12.6 volts.
Then I connect a multimeter, with a min max selection on voltage. go threw the cycle, and start it and the voltage should not go below 9.6 volts if it does the battery is week.
If you have driven the vehicle for a while, and the battery voltage with the engine running is above 14.0 volts, shut down the engine and turn on the lights for 5 minutes, start the engine monitoring the voltage, it is warm and the voltage should not go below 9.6 if it does the battery is junk. After it starts monitor the voltage, If it goes up above 14 volts real quick the battery is sulfated.
 
#7 ·
So is the alternator voltage regulator *smart*? IOW, does it adjust its output voltage based on battery condition? Or should it always be 14V?

Thanks.
 
#9 ·
Despite a lot of people stating that our alternators adjust voltage through smart technology, the truth is the voltage drops due to the self contained unit getting hot. Not an abnormal condition. And once it does it's normal for the voltage output to be about 13.6 vdc, down from the typical 14.2 vdc when cold.

Another word of caution is to check any meter you have against a few others to make sure it reading is correct. We had one well brand (Fluke) at work that was down a few decimals. I've bought an eBay power port reader that showed 0.5 vdc below correct.
 
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#8 ·
The alternator in My Duramax does increase the voltage when it is charging then goes back to 14.0 volts. Most alternators in automotive, put out 15 volts, in class eights they put out in the 14.2 area. When the battery is sulfated it does not get a full charge, and will come up to full voltage easily.
Charging systems, can be compromised by dirty connections, very easily. If the connections have a resistance of .3 volts on each connection that is .6 so a system set to 14.2 is only getting 13.6 actual voltage to the battery, and it will not be fully charged. Also when you want to start the battery is working off 12 volts or lower instead of 12.6.
A voltage drop test will help but a side post battery is difficult to get accurate reading.
Clean soldered connections, and then protected with Die-electric grease, that works.
 
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#10 ·
What about the batteries being connected together? I tested mine the other day, key off , and they showed good. Then isolated one ground and they dropped to marginal
 
#12 ·
First off an alternator putting out 13.6 will not fully charge a battery. You need a minimum of 13.8.
If you have two batteries it is a good thing to separate them and with a regulated charger charge them up to max. Then test them!
I do not have one but when I was at Freightliner they had one of those computerized testers they worked great.
If you have one old and one new battery, they will charge differently.
I have seen units that we had to swap the batteries every three months, to keep them from killing one and boiling the other.
I am going to put my own truck in the shop and separate my batteries and charge them. It is suppose to be a cold winter hear.
Doing a voltage drop test on every connection will find most problems.
I have at least 6 meters, from the best to the cheapest, they are accurate except one I got from Caterpillar, it is useless.
 
#13 ·
It was nice hear today so I separated my batteries and put them on charge, while I did some clean up and changed the remote transmission filter. The one on the left front to a couple of hours to come up to full charge, the one on the right rear took 15 minutes. I was amazed I do use the left battery for boosting. I guess this is where I am suppose to tell you how idles better or I get better fuel mileage. I feel better and believe it will start better if I really need it this winter.
Just a thought! I will be doing it spring and fall from now on.
 
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