2017 5.0L with approx 100K miles on it. 2 year old AGM battery. I have a volt meter installed where cigarette lighter used to be on dash. It normally hovers around 13.5v - 13.9v when cruising at steady speeds with light throttle. Recently I noticed that the voltage spikes to 14.9, sometimes 15v when accelerating moderately to heavy. Question is this voltage spike normal? My assumption is that the voltage regulator should keep the voltage somewhat steady regardless of throttle input. What do you guys think?

 

Yes, the spike is normal. You may also see it drop near 12 while sitting idling in traffic.

 

The BMS signals the Target Battery State of Charge and the alternator regulator adjusts charge percentage as required.

Since your battery is only 2 years old, is it possible that BEFORE that old battery was replaced, you modified the target battery state of charge to more than 80%? If yes the Gencom/Genmon can push the charge voltage to above 15v.

After a long drive, what does your voltmeter show with engine off, ignition on? That could determine your battery life.

 

Hi Russell, actually I did reset the target battery state of charge to more than 80% when it was new, but quickly changed it back to the OEM setting which is 70% if I recall. I completed 1K trip last night, so I thought battery would be topped off. But I just now checked the voltmeter with engine and accessories all turned off, and ignition on as you said, and I was surprised to see it 12.0v. It is a Duracell AGM from Batteries Plus. I had hoped to get more than 2 years out of it, but it looks like its time to replace it. Maybe I cooked it by temporarily setting SOC to 80% at one point. Pretty sure it got hot because the vent caps had pushed up slightly, and that's when I reset the SOC back to OEM.

 

I have a 2019 5.0 and I just changed mine from 80 to 90% and put it back to 80 after I replaced battery yesterday.

I bought the oem motorcraft BAGM-94RH7-800 36 Month battery from ford.oempartsonline.com for $207 plus tax and core, yesterday

I've been buying all my parts from them and picking up at the my local Ford dealer. Prices are around 25-30% less and no fees for using credit card.

If your Duracell AGM had 2 year warranty, that's all it will last, IMHO. My motorcraft was the original battery manufactured in 2019. It still holds 12.2 volts but I waa getting failure messages on the dash. Drive Cycle not available, Front Camera, TPMS etc etc. No problem starting. But it disabled the auto start stop.

Try putting your Target_SOC to 80% and go for a long drive. Reset your BMS too. See if that buys you time before replacing.

 

Can't charge an AGM above 14.8 volts.
The cells are sealed unless the temperature goes high enough to blow the seals from excess internal pressure. Then it loses electrolyte and Battery becomes near useless.
Testing voltage from a Dash port is coming through the Body Control Module and is about 7 tenth volt lower than the at the Battery terminals.
12 volt is about 50% State of Charge and should still crank and start the engine if the Battery has not aged enough or abused.
No need to have Battery above 12.8 v at the Dash before cranking.
On a 2018, the voltage can be seen on the small dash screen when put into engineering mode and stepped to that display.
You can see pre-start, the drop when cranking and the charge level when running all in one place.
Don't fool with the max state of charge from OEM Level.
.
Note; The charge system is different before 2018 model year.
Good luck.

 

Just wondering. The people that disconnect the plug in the battery terminal to disable the Auto Start Stop, will those batteries charge differently?

 

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Very likely will because the BMS Control has been taken away. No temperature control, no age accounting etc. no reduction in charge just after the engine is started to reduce its load on a cold engine. for a few minutes All these designed in features of the BMS are lost by disconnection.
The Alternator still has a Regulator built in as the only control left.
As a basic device it has no program control except a fixed built-in reference to control from.
Charge is then based on Battery Resistance that drops from discharge and presents a difference of voltage to the Regulator. That difference determines the Alternator output for recharge at any given time.
As the difference in voltage reduces, the charge current reduces, just like old times to just the level required by the vehicle needs.
Good luck.

Those who insist on stopping A-S-S can do so by inserting a test plug into the rear Bumper Trailer 4 prong jack and leave it there. A-S-S is not used for Towing. That's why this works.to fool the control circuit. Only other effect is you lose Back-up guidelines in the display that also are not used for Towing when a trailer is hooked up.

 

Thanks

 

I have the same voltage monitor in my 2020 cigarette plug and it does go to 15.0V sometimes, has done that since new. Also commonly goes under 12.0V when it shuts off at a traffic light. It's a wider range of voltages than I expected, but the behaviour hasn't changed over time.

 

UPDATE: Had the battery and charging system tested at the local Batteries Plus store, and everything checked out fine. I experienced none of the symptoms yesterday on a 50 mile drive that I had while on my 800 mile trip home towing my new trailer 2 days ago. I also had my Dometic refrigerator plugged in during the trip, but that's nothing new, have had that for several years now with zero issues. I'm beginning to think the erratic voltage behavior had something to do with the new trailer, but can't imagine what. Its a small 6 x12 single axle cargo trailer with no brakes or electrical loads of any kind other than lights which all were working fine.

One thing I did notice that was different about this new trailer though, is the lighting. In the lower rear corners, there are small button sized leds that glow when the trailer is connected and the ignition off. At one point I heard a soft buzzing noise near the rear of trailer I thought was odd. At first I had no idea it was even coming from the trailer, until my wife disconnected the 4-way plug from the truck and the buzzing stopped. Got busy with other things and thought no more about it until today. Any ideas what the heck is up with that? Thanks for all the help everyone!

 

Check to see if there is corrosion in the trailer light plugs on your truck.

 

How do you change the the state of charge, And why would you? I have a 17.
My factory battery died 2022 Current battery is 3 years old? Noticed the CCA dropped from 750 to 700 while checking it out getting ready for winter. have to keep an eye on it. .