HYBRID 12V Battery Mystery SOLVED

[SafetyGuy]

@ SafetyGuy,
Did you receive the Trailer Module 26C10 (OTA) update yet?
I received the update on my maverick 25Xl hybrid and my charging problem(same as yours), immediately fixed itself! With or without the plug in hitch brake light!
Please remove your hitch brake light and see what happens.

And one more thing, my MPG (indicated) @ 70mph immediately jumped by 23%. But some of that is related to N.E. Wisconsin's sudden increase in temperature today, 90F. vs 50F. last week before my update.

Yes, I had the trailer module update in April when I had my spring oil change.

I was still having the over 15 volts indicated when driving, initially. I then plugged the hitch light in, headlights on.

I am going to unplug the Hitch light, but not yet...I started with the hitch light and headlights on-all was good.

Today I started without headlights on, all is still indicating that battery and voltage is good.

I will use the truck a couple of more times and then if 12 volt battery voltages are still good I will then unplug the Hitch light to see if I still need it.

One step at a time, and thanks for your suggestion!

Andy

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[durangobiker]

Call the OTA division of Ford (833) 389-0848 and ask for all the required software updates for your vehicle. They'll open a case, and then you go to the dealer with your case number, they can't refuse they have to do them. OTA will follow up with you.

After reading through this entire thread (wondering if all the recent Over-The-Air updates might have helped with my battery issues), I finally picked up the phone and called the OTA division of Ford (833) 389-0848. They were very helpful in looking everything up. They confirmed I still need to take it into the dealership for Service Bulletin 26-2170 released April 16th, 2026. This isn't pushed OTA. The agent said she couldn't see SSM 54785 or 52307.

I then called the dealership who I have already scheduled service with to diagnose my evap check engine light (comes on intermittently) to ask if they'd look into this service bulletin. He could see it but wouldn't fully commit that it is necessary.

I hope this info is helpful to others as it seems that SSM and service bulletins are somewhat different and not everyone is speaking the same language. For those that work for ford, should I ask if SSMs have been addressed? Is the tech at the dealership going to be able to see and address the SSMs or are those resolved by my recent OTA updates?

 

[samspritzer]

@ SafetyGuy,
Did you receive the Trailer Module 26C10 (OTA) update yet?
I received the update on my maverick 25Xl hybrid and my charging problem(same as yours), immediately fixed itself! With or without the plug in hitch brake light!
Please remove your hitch brake light and see what happens.

And one more thing, my MPG (indicated) @ 70mph immediately jumped by 23%. But some of that is related to N.E. Wisconsin's sudden increase in temperature today, 90F. vs 50F. last week before my update.

Speaking of 26C10, has anyone asked the dealer to do it and it wasn't done because "recall not available until 5/29/26"?

 

[Master Blaster]

I totally understand everyone's frustration. A new vehicle should start every time and operate as designed without incident. And as a Ford tech. It's frustrating to not be able to fix a car. But I can also say that I didn't feel bad because I used EVERY resource available. I can also say that Ford hasn't simply been sitting on its hands. They literally sent a field service engineer to OUR dealership after several detailed conversations. The frustrating part was that disconnecting circuit in order to perform the tests would often make the problem disappear mid test. I think the most frustrating thing in THIS particular conversation is that I'm sensing that even though Ford seems to have finally come up with a fix, some are dismissing it without trying it and would rather continue the various "workarounds". I say at least TRY the Ford fix given that they've been waiting for it for years. Another frustrating thing is that the problem isn't universal. The VAST MAJORITY of hybrids operate normally with zero battery issues. But the relative few that have problems are difficult to fix. And also, every Ford fix actually fixes SOME trucks but not all.

Understood, thankyou. Ford promised a fix would be available in 2Q26. Is this still in the pipeline, or are we not going to get the real fix now that they've discovered yet another module with poor software sucking the battery down? Is the ABS fix and yet another ACCM fix going to be it?

 

[HeyBales]

I totally understand everyone's frustration. A new vehicle should start every time and operate as designed without incident. And as a Ford tech. It's frustrating to not be able to fix a car. But I can also say that I didn't feel bad because I used EVERY resource available. I can also say that Ford hasn't simply been sitting on its hands. They literally sent a field service engineer to OUR dealership after several detailed conversations. The frustrating part was that disconnecting circuit in order to perform the tests would often make the problem disappear mid test. I think the most frustrating thing in THIS particular conversation is that I'm sensing that even though Ford seems to have finally come up with a fix, some are dismissing it without trying it and would rather continue the various "workarounds". I say at least TRY the Ford fix given that they've been waiting for it for years. Another frustrating thing is that the problem isn't universal. The VAST MAJORITY of hybrids operate normally with zero battery issues. But the relative few that have problems are difficult to fix. And also, every Ford fix actually fixes SOME trucks but not all.

No disrespect - but you've had your head in the game of the intermittent battery drain too long.

This particular conversation and thread - if you catch the right posts - is clearly showing there is a charging strategy that has NOTHING to do with a battery drain issue.
It's not dismissing that issue - it's showing it's a different issue.

An undercharged battery obviously is going to be effected by a battery drain faster - but 1 night compared to 2 nights - big whoop.
It's dead.

Your Ford solutions to the battery drain will keep a battery from taking hits from a drain - which of course too many of them do effect it and shorten it's life too.
But those don't change the charging strategy (unless that trailer update did).

But so does undercharging shorten a battery life.
The AGM's aren't as badly effected, nor undercharged as much as SLA's.

Would you consider normal battery longevity being shortened an issue?
Vast majority operating normally with zero battery issues is a bold claim.
How many of them happen to operate in a mode this thread discusses - and cause full charging to occur often enough? Unknown to driver the positive effect they are getting.
How many of them happen to hook up to external chargers when ever the lights go off early?
How many just live with battery saver functions enabled to some extent and live with an undercharged battery for years?
How many never report in to dealers for the issue due to initial non-responses?

The fact you keep talking about a fix for battery drain - higher than desired draws, and not what has been shown in this thread that is easy to see really, just shows you are missing the point and dismissing what is happening.

Here's what my BMS system thinks of my battery on Monday when it reached 300 days installed, in max battery save mode due to resting voltage 11.8.
The BMS has logged it's been charged the same amount of Amp hours it's been discharged. (whole figures from rounding likely add up very close)
And I have had 2 self-inflicted bad drains to 35% SOC in there due to doors open/lights on - and it recovered from both of them - to the same undercharged state it was in beforehand.
If there have been battery drains related to ACCM or brakes or other - there is no indication of it because the system has the ability to charge very high and long to recover - to it's programmed strategy of undercharged.
Am I having Zero issues because it still starts the truck?
It ain't going to make it 3 yrs - that's an issue in my book. And no lights for more than mere seconds - that's an issue.
And there have been posters that got your SSM's - and still had the issue THIS thread is talking about.

 

[Mareys]

I would have no problem thanking Ford for there due diligence if or when I hear from Ford or one of there representatives saying,: we have seen on some ford mav hybrids that the charging system is not charging to the correct voltage when the SOC reaches over 90%.
And here is what we are going to do to fix it and this is what its going to charge to.

Or we found on your mav hybrid that your ACCM software is corrupt and we need to update it. this is what it is doing now, and this is what we are going to do, and when were done it will not drain after the power is turned off.

And stop giving this story of "you need to drive more".
Then we should return with a reply, then sell me a vehicle that doesn't have a minimum run time.
Should that be a question that we ask the salesman when were interested in a ford mav hybrid? " Does this truck have a minimum run time to charge the battery?

Give us ford mav hybrid owners some credit that we know whats going on with out truck.
We are not a bunch of dummies.

i specifically asked will this Hybrid be good for someone that is retired and doesnt drive far or often. His answer this is exactly what this truck is meant for! Do you know how many times i was told i wasnt driving enough when bringing back a dead truck! Answer 4x !

 

[Mavster Mechanic]

i specifically asked will this Hybrid be good for someone that is retired and doesnt drive far or often. His answer this is exactly what this truck is meant for! Do you know how many times i was told i wasnt driving enough when bringing back a dead truck! Answer 4x !

Driving more does help.
But only if it is at night (full lamps on) or you attach trailer wiring! (Or run the fan at 6 or 7 which is too fast for my taste most of the time.)

But it's easy to switch on the lamps.
And the truck will beep at you if you shut off the truck and leave them on.

 

[Finnster]

Another question to consider.
Out of the 3 charging "fixes" that are shown (IMO) to correct or ameliorate the charging/12V battery problem, Only plugging in trailer hitch brake light "cures" the problem without ever having to draw any amperage! Hybrids don't necessarily need any pedal braking.
I'm guessing that there is a connection between plugging in a hitch light, and the Trailer Module Update.
We may know for sure once the Trailer Module update is available for MY22-24.

 

[MakinDoForNow]

Another question to consider.
Out of the 3 charging "fixes" that are shown (IMO) to correct or ameliorate the charging/12V battery problem, Only plugging in trailer hitch brake light "cures" the problem without ever having to draw any amperage! Hybrids don't necessarily need any pedal braking.
I'm guessing that there is a connection between plugging in a hitch light, and the Trailer Module Update.
We may know for sure once the Trailer Module update is available for MY22-24.

What if the trailer fix removed the plug the light into plug fix????

 

[Finnster]

What if the trailer fix removed the plug the light into plug fix????

It fixed my 25XL hybrid's battery problem, both with the Hitch brake light plugged in, and also with it removed! Best of both worlds.

 

[El Kabong]

How does one check to see what firmware(s) are in the vehicle? Is something like Forscan needed for this?

 

[Darryl]

No disrespect - but you've had your head in the game of the intermittent battery drain too long.

This particular conversation and thread - if you catch the right posts - is clearly showing there is a charging strategy that has NOTHING to do with a battery drain issue.
It's not dismissing that issue - it's showing it's a different issue.

An undercharged battery obviously is going to be effected by a battery drain faster - but 1 night compared to 2 nights - big whoop.
It's dead.

Your Ford solutions to the battery drain will keep a battery from taking hits from a drain - which of course too many of them do effect it and shorten it's life too.
But those don't change the charging strategy (unless that trailer update did).

But so does undercharging shorten a battery life.
The AGM's aren't as badly effected, nor undercharged as much as SLA's.

Would you consider normal battery longevity being shortened an issue?
Vast majority operating normally with zero battery issues is a bold claim.
How many of them happen to operate in a mode this thread discusses - and cause full charging to occur often enough? Unknown to driver the positive effect they are getting.
How many of them happen to hook up to external chargers when ever the lights go off early?
How many just live with battery saver functions enabled to some extent and live with an undercharged battery for years?
How many never report in to dealers for the issue due to initial non-responses?

The fact you keep talking about a fix for battery drain - higher than desired draws, and not what has been shown in this thread that is easy to see really, just shows you are missing the point and dismissing what is happening.

Here's what my BMS system thinks of my battery on Monday when it reached 300 days installed, in max battery save mode due to resting voltage 11.8.
The BMS has logged it's been charged the same amount of Amp hours it's been discharged. (whole figures from rounding likely add up very close)
And I have had 2 self-inflicted bad drains to 35% SOC in there due to doors open/lights on - and it recovered from both of them - to the same undercharged state it was in beforehand.
If there have been battery drains related to ACCM or brakes or other - there is no indication of it because the system has the ability to charge very high and long to recover - to it's programmed strategy of undercharged.
Am I having Zero issues because it still starts the truck?
It ain't going to make it 3 yrs - that's an issue in my book. And no lights for more than mere seconds - that's an issue.
And there have been posters that got your SSM's - and still had the issue THIS thread is talking about.

Unless they had it done AFTER April 8, 2026, they did NOT have it done. But if a person has low charging voltage that's a DIFFERENT problem that might be a repairable problem such as a faulty DC/DC converter. All I'm saying is that in EVERY case of short battery life I've experienced, it's because the battery actually drained. And any case of undercharging, it's been a DC/DC converter. (Rare) . You may indeed have a different problem. But I'd recommend the having the updates done anyway just to see what happens. It can't hurt. Especially if the vehicle is still under warranty.

 

[Darryl]

Sure.

But it's super inconvenient and generally unpleasant to go to a dealership. Some of us work 40-50-60 hour weeks and very few dealerships are open weekend anymore.

The headlamps / parking lamps on is a great temporary fix.

I'll get to a dealer when I NEED to.
I don't need it right now.

Ok. But IF there's a fix that is available that will allow the vehicle to be driven as designed, why not get it, especially if still under warranty? Some dealerships will even drop you off and pick you up if you're close enough to the dealership.

 

[HeyBales]

Unless they had it done AFTER April 8, 2026, they did NOT have it done. But if a person has low charging voltage that's a DIFFERENT problem that might be a repairable problem such as a faulty DC/DC converter. All I'm saying is that in EVERY case of short battery life I've experienced, it's because the battery actually drained. And any case of undercharging, it's been a DC/DC converter. (Rare) . You may indeed have a different problem. But I'd recommend the having the updates done anyway just to see what happens. It can't hurt. Especially if the vehicle is still under warranty.

You REALLY need to find the posts that show this is not a DCDC issue.
This is not a drain issue.

This is a purposeful strategy.

You could see it too with a scan tool monitoring some PIDs.

12V battery SOC%, and Amps (Battery2 for showing decimal value), and Volts.

You have a nice long drive into work.
If you do NOT have the headlights on, do NOT have the fan speed 6 or above, or NO trailer light - here's what several posters with the tools have reported already. With picture proof.

If your SOC% is good enough it's upwards of 90%, you'll be getting your float charge of below 1 Amp pretty quickly.
When it reaches 92% - you should start showing a Voltage of 12.8, and discharge from your battery, negative Amps.

Keep at that - and it'll discharge to mid 80's% SOC. Then float charge again to 92%.

Or, when at 92% and it starts discharging - turn on your headlights manually.
Now what happens to Amps and SOC%?

That's it.

Regarding what you think my issue is - it's the same issue many see that don't have a bad battery die overnight.

The BMS system using the battery sensor is reading ALL Amp hours going into and out of the battery.
And it sees balance.
If DCDC was undercharging - it would show less charge, more discharge.
And if I had short/partial discharge events from the ACCM or ABS - there would be more discharge then charge. Except if you drive long enough, it can recover.

Now - I do think I have a bad battery sensor and it's getting inaccurate Amps IN/OUT.
But I can't prove it - when I put a multimeter in DC Amp mode inline with the negative cable - the BMS must not see enough resistance or something - it drops to no Amp charge to the battery.
I cannot confirm Amps to see if the battery sensor is correct.
It does report the Volts under the true value, but that's better than reporting a higher than true value at least.

Since you have a long drive into work - you could probably do the above test during a lunch drive borrowing a scanner - you should be about as charged as you'll get.

 

[rslilly76]

What if the trailer fix removed the plug the light into plug fix????

it didn't! I can vouch cause I tried it and received the OTA after and nothing changed.

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