Hey guys,

I'm scratching my head a bit with this and figured I'd see if someone on here can help out.

I have a 2016 F150 XLT with the 5L. A few weeks ago, after the truck sat for a week and a half, it was stone cold dead (not a click, no door locks, absolutely nothing). Put a charger on it and it wasn't reaching full charge even after leaving it on for a few days (smart charger said it was between 75 and 100% of charge but wasn't getting to 100%). I did a parasitic draw test on the truck, and after an hour or two, my draw was 53mA, which seems to be within range. With the "charged" battery, and the truck running, my meter was saying 15.01V. I had driven it to work, parked it inside and only had 11.85V on the battery. Spoke with my closest dealership, and they changed the battery.

Brought the truck home, charged the new battery to 100% (12.8V on the terminals after full charge). Start the truck up and the charging system is still putting out 15.01V at the battery terminals. I spoke to the service department at another dealership (who I had to bring the truck to for some bodyshop warranty work), and they said to let it idle for 30 mins and if the voltage doesn't change, there might be an issue. Let the truck run for the 30mins, and the voltage at the battery terminals is still 15.01V. (I've checked it with 2 different voltage meters to confirm my meters are good). While the truck was at that dealer for the body issues, they looked at the charging system and are saying that it's performing as it should.

I drove the truck over the holidays here quite a bit, including driving it on the highway for 150miles each way, and after getting it home I had 12.18V at the battery terminals with the truck shut off.

Now i'm a bit confused. I have a bit of an electrical background, and 15V seems to be quite high for a charging system to be putting out for a 12V battery. The PCM would control the field excitation to the alternator to keep it producing voltage for the amount of load, but 15V at idle with no heavy loads on the truck? Something doesn't sound quite right to me here. The temperature here has been quite cold lately (-5 to -25degC) but it doesn't seem to be temperature dependant.



Can anyone else confirm what their charging system is putting out on their trucks or what it should be? I feel like with a brand new battery, and driving it for over 2hrs at highway speeds, that 12.2V is low and that my charging system is boiling the crap out of my battery.


Thanks!

 

On the cars I've worked on 13.5-14.5 volts is normal. Other factors such as load, condition of the battery and temperature can factor into it. Given your very cold temps I don't know if this is normal or not.

 

Checking for volts, will not tell you any thing other than a your charging system is working. The question is what are the AMP's being put out by the charging system. I can believe the charging system showing 15v when the truck is running and yes it should go down as your battery is approaching 100% charged. Every time you start the truck, your charging system will probably show 15v since the starting draws lots of amp's to turn over the engine thus reducing the batteries capacity. Also remember a batteries efficiency is marginal as the temperature drops especially below 0.

I would be looking into why a new battery is being drawn down so quickly ?

 

+1 to what Storageman says. The voltage by itself doesn't tell you much other than your charging system is working. 15 volts sounds a little high, but not out of line if the battery had been seriously depleted.

Get yourself a decent AC/DC ammeter that you can clamp around the positive lead going to your battery to verify how much current is going into the battery when the truck is running, and also how much is going out when it's not running.

If your battery is fully charged, and the truck is running, you should measure next to nothing actually going into the battery, as the alternator should be supplying close to 100% OF what the truck needs at that point.

 

I agree with what you're saying here.. 15V at startup? Absolutely. 15V after the truck idling for 30minutes after being started on a fully charged battery is what I have a hard time with. 15V after being on the highway for 2+hours is also what i'm having a bit of a hard time with.

 

And I agree with you, but the alternator was putting out 15V with a fully charged battery. It hasn't once moved from 15V. Charged or discharged. I could accept that it was putting out 15V if the battery was discharged and needed to be charged up. I'm concerned that after charging it completely, that it was still putting out that 15V.

The tech at the dealership said the amperage readings were all within spec for what the truck was doing at the time he ran his test.

I also agree with this statement, but after having driven the truck for 2+ hours, I'd expect a little more than 12.2V from a brand new battery. 15V all the time makes me think that something thinks that the battery is drained and is trying to over charge it.



I'm used to a bit bigger alternators having worked in a few power plants so maybe I'm just thinking vehicle ones operate like the industrial ones and may be wrong. I was expecting to see the alternator output voltage drop as the battery is charged, and if there is no demand on the charging system. If there was a heavy load on the system (dead battery charging) or a huge demand (heating/seats/etc), it would be like what i'm seeing.

 

Rule of thumb for a Battery Voltages is 12.75 volts with Vehicle off no Load and 14.50 volts with it running always check the voltage at the battery. Have AutoZone do a load test of the battery to see what condition the Battery is in.

 

Brand new 2 week old dealer installed battery. 12.8V after being on a charger for a few hours. Battery is good.

 

Temperature makes all the difference.

In order for a flooded lead-acid battery to reach 100% charge it needs to see approx. two (2) volts above and beyond the resting open circuit voltage (OCV). For a sealed maintenance free battery this is 12.80 volts. All the numbers you hear about whenever batteries or charging is discussed are based on 77° F

When charging has reached 100% it's also beneficial now and then for it to "cook" for a few hours at this level. So anyway looking at almost 15 volts to begin with just to break even in the summertime.

If you're only seeing 15.0 volts at the alternator at -13° F below zero charging voltage might be a little low and this would also explain the low state of charge on the battery you're seeing. About 16 volts at ten to twenty below zero won't hurt anything, it's required to get the battery to 100%. In hot weather the opposite problem occurs. Charging voltages need to be reduced.

It sure won't hurt anything to charge a battery with an external charger either, in cold weather a battery's internal resistance goes way up so it takes a long time for a battery to charge. It's just about impossible to "boil a battery" at ten below zero. In fact at those kind of temps 14 ~15 volts is basically just a float charge. A "smart charger" may act stupid when it gets real cold, too. They work well for maintenance, not always well for heavy duty charging. Bottom line is battery voltage and charging voltage have to be corrected for temperature. Hope this helps.

 

Good info. Thanks.

 

Most generic electronic test equipment has an accuracy of +/- 10%.

 

What are you stating ??? This thread is not about test equipment its about a battery problem the OP has in low temp conditions !!!

 

Do you Guys Agree that the Voltage Regulator in the Alternator could be Failing I once had a Alternator Putting out Higher Voltage and the Voltage Regulator was at Fault, But a half a volt is not allot, Also have you turned everything on,A Full Load and see if the output voltage goes down?

 

No, at least not the way you're suggesting. Internal battery resistance goes up as the temperature goes down.

Consequently the correct charging voltage is a moving target. If one doesn't understand this, it will never make sense.

When it is 100 degrees F 15 volts will boil a battery, when it's 10 degrees below zero 15 volts is a float charge. Hope this helps.

 

Not enough information to make an informed opinion. I would be checking both volts and amps, and temps, and state of charge.