HYBRID 12V Battery Mystery SOLVED

[Hootbro]

This isn't normal. I leave a trailer and or hitch light pugged in for weeks at a time. Keeps my battery 100% 100% of the time.

Plugged in and sits without driving or plugged in and daily driven?

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[SafetyGuy]

I would not recommend the trailer hitch light trick for a truck that sits. Last Friday afternoon I rented a Uhaul trailer that I left hooked up on the 4 pin overnight and the discharge curve was steep. Truck did start right up the next morning with no warning and charged fine.

Good day @Hootbro

Hmmm, interesting. My thoughts run to possible causes of your drop in battery voltage.

First thought I have is that the trailer may have had an electrical issue, but I would think once you turn power off on your truck, that circuit should not be "awake"? I leave my hitch light in and have not ever noticed a similar depletion.

2nd thought is isolation. Can you plug on another trailer (or light that plugs in to your trailer plug)? Reason being, we are trying to see if the event is repeatable....or was it a faulty trailer...

It looks like you had the trailer plugged in for several days, but only discharged over one night?

If true, then was it coincidence that you happened to have a occasional deep parasitic draw down of the battery?
I am only looking at your provided charts so I may have interpreted incorrectly.

So my next question is, have you had all the module updates that @Darryl has been pounding the drum over, trying to get done if an instance like this happens and your battery is suddenly depleted?

You have the monitor, so that makes this very interesting to me.

Did you see the trailer lights on in the night after you shut down, when they shouldn't be, by any chance? You would have said it, but just covering all the possibilities. If so, then there is a problem in the truck that the trailer circuit is still energized. I know my trailer plug light is never illuminated once I shut down.

Again, it is my belief that once the truck is turned off that the trailer circuit would be open, as we don't want an attached trailer with an electrical fault to kill the start battery!

Anyways, interesting stuff. I hope we can figure out what happened in your instance, and have yourself a good day!

Andy

Edit to add...when troubleshooting an issue, I was taught to try to break the system in halves. In this case, that would be the trailer plug in your truck...if you plug in another trailer, (or voltage meter) and you get the same issue, it is the truck that is responsible.

If the problem disappears, it is most likely the trailer responsible.

And if it an occasional excessive parasitic drain, definitely get the module updates done ASAP.

 

[Finnster]

Great knowledge base on this forum, this topic no exception. Most posters have 22-24MY Mavericks with FLA OEM installed batteries. I have a 25MY hybrid purchased April 2025, OEM equipped AGM. Currently have 13k miles, never a 12V problem. My car scanner shows consistant 14.3V charging voltage while driving, never dropping below. Driving with headlights on makes no appreciable difference in 12V charging current, only an uptick in DC converter current to make up the headlight current draw. So, I'm not experiencing12v battery failure, headlight on/off state seeming immaterial, and car scanner showing a very minor 8ma quiescent 12v battery current (very low) - what does all this mean? Was there a 25MY charging algorithm update, am I just lucky, waiting on my eventual 12V battery to fail prematurely?

Great knowledge base on this forum, this topic no exception. Most posters have 22-24MY Mavericks with FLA OEM installed batteries. I have a 25MY hybrid purchased April 2025, OEM equipped AGM. Currently have 13k miles, never a 12V problem. My car scanner shows consistant 14.3V charging voltage while driving, never dropping below. Driving with headlights on makes no appreciable difference in 12V charging current, only an uptick in DC converter current to make up the headlight current draw. So, I'm not experiencing12v battery failure, headlight on/off state seeming immaterial, and car scanner showing a very minor 8ma quiescent 12v battery current (very low) - what does all this mean? Was there a 25MY charging algorithm update, am I just lucky, waiting on my eventual 12V battery to fail prematurely?

My guess is that you are just lucky at this point. Your battery hasn't been significantly damaged at this point yet! Mou must have gotten a good battery from the factory!

My battery was junk right from the factory! Probably underfilled, like some other fluids.

My starting charging voltage when I picked up the new truck 6-13-26 was about 14.8V, if I recall correctly. Within about 2-3 months the charging voltage had slowly risen to 15.1, topping out at 15.4.
I then started using a Noco 1 maintainer to fully recharge the battery once a week or so!
I plan to just limp this battery along until It's nearing the end of the warranty period, then see if I can get a replacement.

And now back to Nascar on Prime.

 

[Hootbro]

First thought I have is that the trailer may have had an electrical issue, but I would think once you turn power off on your truck, that circuit should not be "awake"? I leave my hitch light in and have not ever noticed a similar depletion.

Nothing was discernable to me that it would have a electrical issue. Trailer was relatively new looking and pass all light checks when hooked up and nothing status on the dash that there was anything to indicate a light problem.

2nd thought is isolation. Can you plug on another trailer (or light that plugs in to your trailer plug)? Reason being, we are trying to see if the event is repeatable....or was it a faulty trailer...

I have nothing else at the moment to plug in and try to repeat the situation. Does pique my interest to possibly getting or making a dummy load to hook to the 4 pin. Do not have 4K package so no 7 pin connector, just the 4 pin.

It looks like you had the trailer plugged in for several days, but only discharged over one night?

Trailer was only plugged in for less than 24 hours at the two red points on the graph. It sat shut off from 3:00PM on Friday until I started it at 5:30AM on Saturday and that is marked at the low point of the graph and then drove it and delivered what I was hauling and turned it in at 1:00 PM on Saturday.

So my next question is, have you had all the module updates that @Darryl has been pounding the drum over, trying to get done if an instance like this happens and your battery is suddenly depleted?

My truck has a 2/27/2026 build date and would assume it has the latest coverage until that point for updates. I did briefly a week ago had a Ford Service subscription and it showed no available updates other than something for ABS.

Did you see the trailer lights on in the night after you shut down, when they shouldn't be, by any chance? You would have said it, but just covering all the possibilities. If so, then there is a problem in the truck that the trailer circuit is still energized. I know my trailer plug light is never illuminated once I shut down.

Only lights that stayed on were the normal exterior marker lights that stay on a few seconds after shutting off and exiting the vehicle. Nothing was noticeable staying on after that.

Again, it is my belief that once the truck is turned off that the trailer circuit would be open, as we don't want an attached trailer with an electrical fault to kill the start battery!

I would normally think that also but after looking at the schematics for the trailer system, it is not as analog as other vehicles in the past and goes into the Trailer Tow Module, battery junction box and a blackhole of whatever circuitry controls them.

 

[SafetyGuy]

Nothing was discernable to me that it would have a electrical issue. Trailer was relatively new looking and pass all light checks when hooked up and nothing status on the dash that there was anything to indicate a light problem.


I have nothing else at the moment to plug in and try to repeat the situation. Does pique my interest to possibly getting or making a dummy load to hook to the 4 pin. Do not have 4K package so no 7 pin connector, just the 4 pin.



Trailed was only plugged in for less than 24 hours at the two red points on the graph. It sat shut off from 3:00PM on Friday until I started it at 5:30AM on Saturday and that is marked at the low point of the graph and then drove it and delivered what I was hauling and turned it in at 1:00 PM on Saturday.

My truck has a 2/27/2026 build date and would assume it has the latest coverage until that point for updates. I did briefly a week ago had a Ford Service subscription and it showed no available updates other than something for ABS.


Only lights that stayed on were the normal exterior marker lights that stay on a few seconds after shutting off and exiting the vehicle. Nothing was noticeable staying on after that.



I would normally think that also but after looking at the schematics for the trailer system, it is not as analog as other vehicles in the past and goes into the Trailer Tow Module, battery junction box and a blackhole of whatever circuitry controls them.

Thank you for all your clear answers, even though it does have me scratching my head.

I have the tow pkg, but my Hitch light is plugged into my 4 pin trailer plug.

I know I have had one in the past, and it is a simple 4 pin trailer plug tester. Inexpensive, cheaper even then a simple trailer plug in Hitch light to see if plugging anything at all into your trailer plug initiates a 12 volt power drain.

Yours is a 2026 and 4 pin only, so possible a different trailer plug gremlin is raising its head, but let's keep things simple as possible by trying out a simple trailer plug light or similar, and see what your monitor tells you!

I know I probably lent my 4 pin tester out to someone in need, and promptly forgot that I had done that...par for the course, but next time I am at Canadian Tire I will be looking for a replacement lite checker, as now I am missing it for test purposes!

I hope we hear back from you if you try any tests or tow again (or just plug a stray trailer into your truck for test purposes), as this is very interesting and I am always interested in trying to find out what it is and fix these tricky issues.

(Final thought, if it a new gremlin related to battery drain, it is a good time to try and figure out if there is an issue, and get Ford to sort it as you have that monitor to validate your concerns...warranty is the best way to not waste your own money on something).

Cheers,

Andy

 

[KenE]

My guess is that you are just lucky at this point. Your battery hasn't been significantly damaged at this point yet! Mou must have gotten a good battery from the factory!

My battery was junk right from the factory! Probably underfilled, like some other fluids.

My starting charging voltage when I picked up the new truck 6-13-26 was about 14.8V, if I recall correctly. Within about 2-3 months the charging voltage had slowly risen to 15.1, topping out at 15.4.
I then started using a Noco 1 maintainer to fully recharge the battery once a week or so!
I plan to just limp this battery along until It's nearing the end of the warranty period, then see if I can get a replacement.

And now back to Nascar on Prime.

I accept that I may be lucky at this point. Also on my side is stable operating environment compared to folks living year round either too far North or South, temperature extremes. We spend six months in Kentucky, six winter months in south Texas.

 

[HeyBales]

Great knowledge base on this forum, this topic no exception. Most posters have 22-24MY Mavericks with FLA OEM installed batteries. I have a 25MY hybrid purchased April 2025, OEM equipped AGM. Currently have 13k miles, never a 12V problem. My car scanner shows consistant 14.3V charging voltage while driving, never dropping below. Driving with headlights on makes no appreciable difference in 12V charging current, only an uptick in DC converter current to make up the headlight current draw. So, I'm not experiencing12v battery failure, headlight on/off state seeming immaterial, and car scanner showing a very minor 8ma quiescent 12v battery current (very low) - what does all this mean? Was there a 25MY charging algorithm update, am I just lucky, waiting on my eventual 12V battery to fail prematurely?

Your current battery with current driving times can't reach 92% SOC.
Actually, can't reach it appears mid/high 80's%.

So the hacks won't work for you.

SafetyGuy got a battery charge at dealership during his software update probably - allowed his to be high enough when he took it back - and hacks have worked as expected.

8 mA - that's excellent. That's from the previous sleep period - I'm guessing a long one, not like during errands for 1 hr.
You have Fuse 11 plugged in?
If so - must have great AT&T cell signal where truck is at.

From other posters with scanners or Voltage reading to discern - doesn't appear to be a change to charging scheme. Same thing this thread points out.

What did change according to manual - 25/26 now have the hybrid with some entered battery spec's (like the EB has been), not totally needing to be estimated during a learned sleep period. So more accurate on what the SOC is when you actually can do math with expected Ah battery figure.

 

[Finnster]

I accept that I may be lucky at this point. Also on my side is stable operating environment compared to folks living year round either too far North or South, temperature extremes. We spend six months in Kentucky, six winter months in south Texas.

That explains a lot!
Thanks for the info. Freezing cold temperatures seems to have a huge negative effect on the Mav's 12V battery!

 

[KenE]

Your current battery with current driving times can't reach 92% SOC.
Actually, can't reach it appears mid/high 80's%.

So the hacks won't work for you.

SafetyGuy got a battery charge at dealership during his software update probably - allowed his to be high enough when he took it back - and hacks have worked as expected.

8 mA - that's excellent. That's from the previous sleep period - I'm guessing a long one, not like during errands for 1 hr.
You have Fuse 11 plugged in?
If so - must have great AT&T cell signal where truck is at.

From other posters with scanners or Voltage reading to discern - doesn't appear to be a change to charging scheme. Same thing this thread points out.

What did change according to manual - 25/26 now have the hybrid with some entered battery spec's (like the EB has been), not totally needing to be estimated during a learned sleep period. So more accurate on what the SOC is when you actually can do math with expected Ah battery figure.

Yes, F11 is plugged in and AT&T service is excellent where we reside in KY, where the Mav is parked, just inside pole barn. I'm going to use my NOCO 5 to charge battery for a day straight, try the hack with lights, check resting g 12v with hood open after Mav sits over ight, etc; to see if resting boltage improves.

 

[rslilly76]

Update:

100% battery charge for more than 60 consecutive days. No help from external charger. Only lamps on each drive.

I'm assuming everything else about the hybrid is working correctly?

I can't get mine over 98% but I wonder if it's cause I drove a year not doing this?

 

[rslilly76]

So, what are you doing that the rest of us are not? I have all updates and TSBs done, have a Motorcraft AGM battery about 6 months old in my 23 Hybrid, and always read 14.3V when charging and 12.1V a half hour after shutting it off. That's only a 70% charge on an AGM battery.

turning the lights on is all he's doing

 

[MakinDoForNow]

That explains a lot!
Thanks for the info. Freezing cold temperatures seems to have a huge negative effect on the Mav's 12V battery!

As a lead acid battery discharges the specific gravity of the electrolyte reduces which allows ice crystals to form at a higher temperature than a fully charged battery. A deep cycle battery will (generally) have a purer lead and an electrolyte with a higher initial specific gravity so it will not suffer from freezing temps as easily as a standard battery. An agm battery will handle colder temps due to its higher specific gravity and less fluid electrolyte.

 

[inline_five]

2023 xlt

I'm getting some massive drawdowns after parking in my garage randomly. Not all the time, but it does happen. When I park I always turn off HVAC controls before turning off the vehicle. F11 is in and ATT service is excellent here.

You can see it on June 10th, 12th, and 13th. Without these massive drawdowns the battery would be great. My warranty runs out in Sept and apparently Ford will charge shop time to apply a fix (terrible customer service) so hopefully they figure it out before then.

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