HYBRID 12V Battery Mystery SOLVED

[rslilly76]

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.

my 25XL received the OTA trailer update, the truck still discharges at 92% unless you do one of the 4 things to keep it charging.

So what do you mean it fixed yours?

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[Red Eyes - Wide Shut]

I do believe the problem is not fixed. It has been somehow drawn out to a longer time to keep customers from going back during the warranty coverage period. They are treading a line of creating a condition that makes the owner deal with and accept premature battery failure as a normal hybrid function.

 

[johnDeere]

Well there is 36 pages about this issue.
It now looks like one of the main issues is the charging voltage.
We know what the charging voltage is. (15.X).

But I have not seen what the floating voltage SHOULD be?

We see what the floating voltage is when it reaches over 91%, and it 12.8V
It looks like a lot of owners have seen this voltage, (12.8), so it not a fluke to me.
Is there a update for the BMS so the floating voltage is higher and what ford thinks it should be?
And what should it be, all I know it must be higher than 12.8V

 

[Finnster]

my 25XL received the OTA trailer update, the truck still discharges at 92% unless you do one of the 4 things to keep it charging.

So what do you mean it fixed yours?

The only gauge of battery charging and 12V battery condition is my plug-in powerpoint voltage display, which agrees with my multimeter within 0.1V.
Using the plugin voltage display, before the trailer module OTA my running 12V voltage always showed 15.1 - 15.4 volts at the battery (this is the exact same thing that @SafetyGuy has reported on his 2025 hybrid before hitch light install and possibly with OTA only).
I didn't get to test the hitch brake light before the OTA, so I can't speak to that.
But upon initial start after OTA, My shown voltage completely normalized - instead of jumping to 15.1 volts indicated as it had done since new, It now jumped to 14.8V which is a normal charging voltage! I have driven the truck about five times since OTA and the 12V voltage hasn't gone above 14.8 Volts!
At the end of a 30 mile highway trip yesterday I noticed that my 12V battery voltage indication had come down to 14.1, Indicating to me that the 12V battery was now fully charged.
IMO Fixed!
Also, immediately upon OTA my gas mileage has improved. Very rough data is that at a steady 70mph mpg increased from 30mpg to 33-37mpg. too early to be sure. Secondary roads (35-45MPH) has also increased some up 45ish to 50ish?, and that overall mileage includes about 30 to 50% city driving. - not enough data yet.
All numbers are indicated from the dashboard displays.
All very limited data form one week of driving after the update! YMMV.
Update - I just checked my 12V battery's state of charge after a one-hour rest. It is now sitting at 88% SOC, whereas before the trailer update it had been at 50% SOC after a one hour rest!
All circumstantial evidence, but it looks good to me!

 

[Mavster Mechanic]

Well there is 36 pages about this issue.
It now looks like one of the main issues is the charging voltage.
We know what the charging voltage is. (15.X).

But I have not seen what the floating voltage SHOULD be?

We see what the floating voltage is when it reaches over 91%, and it 12.8V
It looks like a lot of owners have seen this voltage, (12.8), so it not a fluke to me.
Is there a update for the BMS so the floating voltage is higher and what ford thinks it should be?
And what should it be, all I know it must be higher than 12.8V

During the "draw down" period, when the battery is between 92% and 100% I have seen the DC/DC shut off completely. At least that's how I interpret it.

Negative 22A to 25A coming out of the 12v and voltage pulled down by the load to 12.1, 12.0, 11.9 volts.

ON A BRAND NEW BATTERY.

(Lights on keeps it 100% charged.)

Rain keeps it 100% charged too!

Rain = wipers.
Wipers = headlamps come on in daytime.
Headlamps on automatically in the daytime charged mine to 100% today.

 

[johnDeere]

During the "draw down" period, when the battery is between 92% and 100% I have seen the DC/DC shut off completely. At least that's how I interpret it.

Negative 22A to 25A coming out of the 12v and voltage pulled down by the load to 12.1, 12.0, 11.9 volts.

ON A BRAND NEW BATTERY.

(Lights on keeps it 100% charged.)

Rain keeps it 100% charged too!

Rain = wipers.
Wipers = headlamps come on in daytime.
Headlamps on automatically in the daytime charged mine to 100% today.

As for my 2023 mav hybrid XLT
When the SOC reached over 91% the charging voltage dropped to 12.8 but when the SOC dropped down to less than 89% the charging voltage jumped back up to 14.X volts.
And a bunch of charging takes place.
As for what you said the dc/dc converter shut off, from what I am seeing on car scanner, ( I have a PID set for HVB to LVB current), I can see the converter is still sending current to the system, but not to the battery, since the voltage is so low. I have a PID for 12 V battery current too.
So the dc to dc converter is still making 12+ voltage.

 

[Finnster]

.... (Lights on keeps it 100% charged.)

Rain keeps it 100% charged too!

Rain = wipers.
Wipers = headlamps come on in daytime.
Headlamps on automatically in the daytime charged mine to 100% today.

OMG, In one of my earlier posts on this subject I had stated that none of these hacks had changed my 2025 Maverick's 12V running at 15.1 - 15.4V!
Now I remember that I had a "freak" occurance a month or so back.
I happened to notice that my indicated voltage had dropped from 15.1V to 14.8V and held there till the end of my short trip - I believe it was also raining that day!

 

[El Kabong]

Interesting non-Ford news or not? A class action lawsuit against Subaru over parasitic drain problems....

https://topclassactions.com/lawsuit...ms-vehicles-have-defective-electrical-system/

 

[MakinDoForNow]

OMG, In one of my earlier posts on this subject I had stated that none of these hacks had changed my 2025 Maverick's 12V running at 15.1 - 15.4V!
Now I remember that I had a "freak" occurance a month or so back.
I happened to notice that my indicated voltage had dropped from 15.1V to 14.8V and held there till the end of my short trip - I believe it was also raining that day!

Plus ambient temp (70-72°F?) was above the turn on 15.1 volt dcdc rate for heaters which would not be needed unless temps were below 68-80°F. Whatever temps trigger the higher buss voltages.
ETA: am currently driving 75 mph in outside air temp of 91°F with power point buss reading to g 14.7 volts.

 

[HeyBales]

The only gauge of battery charging and 12V battery condition is my plug-in powerpoint voltage display, which agrees with my multimeter within 0.1V.
Using the plugin voltage display, before the trailer module OTA my running 12V voltage always showed 15.1 - 15.4 volts at the battery (this is the exact same thing that @SafetyGuy has reported on his 2025 hybrid before hitch light install and possibly with OTA only).
I didn't get to test the hitch brake light before the OTA, so I can't speak to that.
But upon initial start after OTA, My shown voltage completely normalized - instead of jumping to 15.1 volts indicated as it had done since new, It now jumped to 14.8V which is a normal charging voltage! I have driven the truck about five times since OTA and the 12V voltage hasn't gone above 14.8 Volts!
At the end of a 30 mile highway trip yesterday I noticed that my 12V battery voltage indication had come down to 14.1, Indicating to me that the 12V battery was now fully charged.
IMO Fixed!
Also, immediately upon OTA my gas mileage has improved. Very rough data is that at a steady 70mph mpg increased from 30mpg to 33-37mpg. too early to be sure. Secondary roads (35-45MPH) has also increased some up 45ish to 50ish?, and that overall mileage includes about 30 to 50% city driving. - not enough data yet.
All numbers are indicated from the dashboard displays.
All very limited data form one week of driving after the update! YMMV.
Update - I just checked my 12V battery's state of charge after a one-hour rest. It is now sitting at 88% SOC, whereas before the trailer update it had been at 50% SOC after a one hour rest!
All circumstantial evidence, but it looks good to me!

So being at 50% SOC would sure explain the 15.x V charging level.

So after OTA with those above figures of 14.xV and improved mileage - you are using the trailer hitch light?

 

[HeyBales]

Interesting non-Ford news or not? A class action lawsuit against Subaru over parasitic drain problems....

https://topclassactions.com/lawsuit...ms-vehicles-have-defective-electrical-system/

Ouch - TSB's sound like they were trying to remedy it, through oh so many years.
Yikes - at that point is when you really do design a master module that looks for power draws to other modules - and shuts off power to them when they should be shut down or less power.
Obviously they do it for lights, radios to some degree, ect.
And more sensors and more monitoring just means more can go off the rails.
But still.

 

[Finnster]

So being at 50% SOC would sure explain the 15.x V charging level.

So after OTA with those above figures of 14.xV and improved mileage - you are using the trailer hitch light?

No trailer hitch light!
I will start using hitch brake light tomorrow to confirm that the 12V battery voltage stays at 14.1 - 14.8V.
Again, these are all early results/observations, It only being a week of post OTA trailer module update!
I only put 0 to 30ish miles on the truck per day.

 

[HeyBales]

No trailer hitch light!
I will start using hitch brake light tomorrow to confirm that the 12V battery voltage stays at 14.1 - 14.8V.
Again, these are all early results/observations, It only being a week of post OTA trailer module update!
I only put 0 to 30ish miles on the truck per day.

I'd bet you are getting the float level charge up to 92% SOC. But never reaching it.
Before you were getting the higher charge to get up to 88%. But didn't go over.

What has your morning resting Voltage been?
I know, you gotta turn on then off quickly, so a tad bit of charge - but still.

 

[Finnster]

I'd bet you are getting the float level charge up to 92% SOC. But never reaching it.
Before you were getting the higher charge to get up to 88%. But didn't go over.

What has your morning resting Voltage been?
I know, you gotta turn on then off quickly, so a tad bit of charge - but still.

Pre Update:
Morning voltage after 12-18 hours rest: 12.1 - 12.2V

Resting SOC(battery tester, at battery) after 1 hour rest after a short trip: 50%.

Post Update:
Morning voltage after 12-18 hours rest: 12.3 to 12.4V.
12V battery has already been damaged at 11 months old.

Resting SOC(battery tester, at battery) after 1 hour rest after a short trip: 88%. Measured only once,(this morning).

Note - I haven't charged or touched the 12V battery since my last SOC check before the trailer module update. SOC, etc. all improved spontaneously.

As much as I like the effects of the update that I believe I am seeing, it is a shame that it had to come before I got a chance to do some decent testing before it arrived.

I will soon be switching to my summer wheels with well-worn tires and that will change my MPG's again, further clouding the subject in my case!

My deepest thanks to @ Mavster Mechanic!
Awesome detective work and gracious follow-through!

 

[El Kabong]

Morning voltage after 12-18 hours rest: 12.3 to 12.4V.
12V battery has already been damaged at 11 months old.

IIRC an AGM battery can be trickle charged back to better health but it can only be done very slowly (<3 amps with a dedicated trickle charger). At least, this was possible on the tiny battery in my used Miata a couple of decades ago.

Worth a shot in any case.

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