I know the BMS demands more or less at times, is driving at 12.9 normal? When I let off the gas it goes up to 14.

 

Good question How did you track the voltage? Did you use the engineering mode?

 

That as well as the SCT tuner when I have it with me. The battery is the original one at 4 years old.

 

Normal running voltage is 14 to 14.7 depending on the battery charge and state of health.
The BMS controls the charge rate based on battery temperature, state of charge (difference between the battery voltage and the reference) after starting, and battery impedance.
there may be a DTC code for the battery/Alternator control, Alternator issue or battery issue.
It may be possible the Sensor at the Neg terminal is in faults.
Don't rule out more than one fault at the same time.
The system needs to be gone over to see what the issue is.
Don't throw parts at the problem until the fault is proven.
Good luck.

 

For a car without a BMS though, im trying to figure out of 12.9 is normal for the BMS, I rarely get above 14 volts when driving

 

.
What are we talking about?
Your original post did not say that.
What year are you inquiring about.
There are three different control systems and years they are used.
Before the 2004 there was no control system except the normal Alternator/ Regulator system used on Flooded Lead Acid battery.
It was not possible to use a BMS system before OBD II CAN BUS system was switched to in 2004. Then these systems came in as updates and more features were added, as the years passed.
Still, the normal voltage range running is over 14 volts in a fault free system for either an FLA or a AGM battery in any of the three systems.
Its the type of battery and the control requirements that are different to service the other systems on the vehicle.
Be specific so the correct answer can be offered for the application you are referring to.

 

My truck is in my signature. I put it there for a reason.

14 constant volts is for cars without a BMS. Its perfectly normal for our trucks to run below 14, im trying to figure out if 12.9 was an indication of a problem. Its not that hard to understand

 

Let me clarify his question. He has a F150 with the BMS system and is wondering if 12.9 v is a normal running voltatge for a fully charged battery on his truck?

He also wants to know what is the running voltage on an unrelated vehicle that he does not own that has no BMS but just a voltage regulator.

 

correct, I didnt think it was difficult to understand lol. Either way, I just put in a new battery and its hanging out at 14.3 constantly. I will see what happens as I drive around

 

And I answered both in detail.
The running voltage has to be above 14.0. Been that way at least since the mid 90s.
If not, the lighting will go dim on 12 volts and brighten up on 14.
That is NOT normal.
Often the Alternator Brushes and or Commutator are worn.