HYBRID 12V Battery Mystery SOLVED

[Hcopter]

Is Aux 12v battery the 12v battery in the maverick or that of a second 12v possibly either for backup or possibly a 12v in a trailer?

I'm not sure why it's listed as "Aux" either, but It's the only 12v SOC sensor I could find listed in the app and it seems to work as expected.

Sponsored

 

[Mavster Mechanic]

I "think" (unproven) one of the recent dealership visits that included recalls and software updates secretly (well, without my knowledge) changed some BMS settings.

With headlamps off, on a one hour drive, my 12v battery is doing this:

Anything above SOC 90% "oh no! Gotta discharge that battery!"

Anything below SOC 88% "oh no! Gotta charge that battery!"

It did several cycles of

87-91-87-91-87-91. LAMPS AND FAN OFF.

Only 3 days of data.

Whether parking at 100% or 87% It still drops 4% or 5% While parked 9 hours at work, or 12 hours overnight at home.

Still, with some lamps on it will go to 100% and stay 100%

 

[durangobiker]

Switching to a hybrid from and eco this coming Friday

New 25 hybrid…What are things I should be looking at or issues I should look out for

My 12V starter battery died within 1 week of delivery. Dealership replaced it as a failed battery, but was terrible to work with even with that. Had truck for a week and even broke the vent tube and didn't own up. Have had 2 TPMS sensors fail/break, but I think that might be due to either carelessness at discount tire or the design of the sensor. I also have lots of issues with the evap system. Not sure how common that is, but neither are fun. I get a dead battery and "deep sleep" if I don't drive for 4 days even with the replaced AGM battery. Good luck!

 

[Mavster Mechanic]

My 12V starter battery died within 1 week of delivery. Dealership replaced it as a failed battery, but was terrible to work with even with that. Had truck for a week and even broke the vent tube and didn't own up. Have had 2 TPMS sensors fail/break, but I think that might be due to either carelessness at discount tire or the design of the sensor. I also have lots of issues with the evap system. Not sure how common that is, but neither are fun. I get a dead battery and "deep sleep" if I don't drive for 4 days even with the replaced AGM battery. Good luck!

So are you going to try driving with headlamps on every drive? Do it for a month. See if deep sleep goes away or reduces.

I think it is supposed to happen by design after 7 days of non use.

 

[durangobiker]

So are you going to try driving with headlamps on every drive? Do it for a month. See if deep sleep goes away or reduces.

I think it is supposed to happen by design after 7 days of non use.

I like the suggestion. I just ordered one of these ODB2 sensors so I can monitor the SOC as the truck sees it. I will note that I've done the tape trick to get it fully juiced in the past, but I don't really think it's often that when I park after a 20 min drive that the voltage is less than 13.1V. What voltage is fully charged on the AGM?

The truck still has a rapid depletion of the battery (less than 7 days) -- I currently use a little bluetooth Voltage monitor, but don't really know how much it is helping me know because voltage curve and battery capacity are non-linear, and the logger stops working when the voltage drops out. See screenshot of March 2nd when the last deep sleep /dead battery occurred. The other screenshot shows normal operation when I don't let it sit.

 

[HeyBales]

Is Aux 12v battery the 12v battery in the maverick or that of a second 12v possibly either for backup or possibly a 12v in a trailer?

My picture above of the PIDs said 2nd battery and that's why I initially never used it, because I saw other PIDs regarding 2nd or Aux battery that I figured were orphaned from an F250, they contained no data.
There would have to be a sensor for a true aux battery hookup - never heard about that.

But the one for Amps actually did read the same - except not rounded to whole numbers only.

 

[HeyBales]

I like the suggestion. I just ordered one of these ODB2 sensors so I can monitor the SOC as the truck sees it. I will note that I've done the tape trick to get it fully juiced in the past, but I don't really think it's often that when I park after a 20 min drive that the voltage is less than 13.1V. What voltage is fully charged on the AGM?

The truck still has a rapid depletion of the battery (less than 7 days) -- I currently use a little bluetooth Voltage monitor, but don't really know how much it is helping me know because voltage curve and battery capacity are non-linear, and the logger stops working when the voltage drops out. See screenshot of March 2nd when the last deep sleep /dead battery occurred. The other screenshot shows normal operation when I don't let it sit.

What are your settings for the OTA functions?
Automatic Nightly checks, weekly, manual only?

Appears that faster drop on the 2nd was after a drive?
Wondering if you had a parasitic drain - several threads on that, which mistakenly include the undercharging this thread is dealing with.
2 software updates the dealer needs to do - one to the ACCM so not OTA available. Not sure if the ABS one is.

 

[MakinDoForNow]

My picture above of the PIDs said 2nd battery and that's why I initially never used it, because I saw other PIDs regarding 2nd or Aux battery that I figured were orphaned from an F250, they contained no data.
There would have to be a sensor for a true aux battery hookup - never heard about that.

But the one for Amps actually did read the same - except not rounded to whole numbers only.

In the fords (f250?) with 2 12v batteries perhaps the sensor is on the negative post. The primary pid may have been the one dropped and would not show as an additional pid. Who knows. If Aux 12v pid gets info updated from the 12v in truck everything is ok.

 

[durangobiker]

What are your settings for the OTA functions?
Automatic Nightly checks, weekly, manual only?

Appears that faster drop on the 2nd was after a drive?
Wondering if you had a parasitic drain - several threads on that, which mistakenly include the undercharging this thread is dealing with.
2 software updates the dealer needs to do - one to the ACCM so not OTA available. Not sure if the ABS one is.

Great questions! I feel a little dumb saying I have no idea if I have the updates you mention. According to the Ford app, my "Automatic Updates" are on nightly, and last update was performed 1/24/26- SW Update 11 - SYNC-25.2.4.9

Logging in to https://www.ford.com/support/software-updates says
Software Update 11 - Connectivity
updated 01/28/2026
TCU-25.2.8.5

Are these the most recent for the 2025 Mavs?

My local dealership works on my vehicle after their demonstration of ineptitude, so I rarely take it in. Last time they did a service was probably 9 months ago and they may have updated the non-OTA update you mentioned then?

Did the updates improve battery drain/deep sleep for others with a 2025, or was that just for the 2024 MY and prior?

 

[HeyBales]

My MY25 XL Hybrid charges the 12V battery full time also (whenever the truck is in "ready mode").
I think there is a different charging scheme between MY22-24, and MY25/26? hybrids.
Maybe we will need a new thread when/if our 12V AGM battery's start to fail.

Considering some with 25 with AGM drivers report the same ability to drop to lower resting voltage/SOC% and BMS seems happy to leave it there - it seems the goal is the same, the method is likely different.

While the pre-25MY hybrids have no battery spec's entered in available PIDs, so the BMS isn't going to be setup to use them, the 25MY went to the EB method of having some spec's entered.
The manual makes this distinction very clear under battery specs.

So the 25MY BMS doesn't have to use Relearn to attempt to calculate What the battery is and how to charge it, perhaps staying on the safe side, but rather Where the battery is in it's life and how to charge it.

Much better ability when it knows what size it is at minimum, but also battery type.

 

[HeyBales]

Great questions! I feel a little dumb saying I have no idea if I have the updates you mention. According to the Ford app, my "Automatic Updates" are on nightly, and last update was performed 1/24/26- SW Update 11 - SYNC-25.2.4.9

Logging in to https://www.ford.com/support/software-updates says
Software Update 11 - Connectivity
updated 01/28/2026
TCU-25.2.8.5

Are these the most recent for the 2025 Mavs?

My local dealership works on my vehicle after their demonstration of ineptitude, so I rarely take it in. Last time they did a service was probably 9 months ago and they may have updated the non-OTA update you mentioned then?

Did the updates improve battery drain/deep sleep for others with a 2025, or was that just for the 2024 MY and prior?

Regarding the OTA questions - I was merely raising that as the fact your truck is connecting nightly it appears and spending power checking.
So a faster drain is expected that you showed - than someone on manual checks, or none.
And depending on signal quality and packet errors - even a simple check could be a power waste as it constantly resends packets.
Throw in a computer glitch going off the rails in that process - would be interesting to see when the nightly checks are, and when you showed that voltage nosedive in the logs.

Those updates aren't recalls - they are SSM's if you have the stated issue - battery drained.
You'll likely see those threads on page 1 or 2 here for more details than this thread.
And yes 25's for them. Hopefully your work order for your battery drain mentions something besides checking battery.

 

[HeyBales]

I "think" (unproven) one of the recent dealership visits that included recalls and software updates secretly (well, without my knowledge) changed some BMS settings.

With headlamps off, on a one hour drive, my 12v battery is doing this:

Anything above SOC 90% "oh no! Gotta discharge that battery!"

Anything below SOC 88% "oh no! Gotta charge that battery!"

It did several cycles of

87-91-87-91-87-91. LAMPS AND FAN OFF.

Only 3 days of data.

Whether parking at 100% or 87% It still drops 4% or 5% While parked 9 hours at work, or 12 hours overnight at home.

Still, with some lamps on it will go to 100% and stay 100%

Must have been.

I only had 1 week with my new warranty replaced battery before it went low enough the goal was no longer 85% it seemed.
But during that week - at 85% it allowed discharge at 12.8V.
But when lower than 80%, once that was reached, it was float charge below 1A and 14.xV.
My trips weren't long enough to hit the high 85% after it allowed dropping to whatever the low was, with only a float charge.
So you got a newer update than 24XLT.

I thought the BCM (which has the BMS function) was updated for the tail light recall. But that was mid-24.
Rear camera wasn't BCM, so that's probably it for me.
You had your batch of recalls more lately?

 

[durangobiker]

Regarding the OTA questions - I was merely raising that as the fact your truck is connecting nightly it appears and spending power checking.
So a faster drain is expected that you showed - than someone on manual checks, or none.
And depending on signal quality and packet errors - even a simple check could be a power waste as it constantly resends packets.
Throw in a computer glitch going off the rails in that process - would be interesting to see when the nightly checks are, and when you showed that voltage nosedive in the logs.

Those updates aren't recalls - they are SSM's if you have the stated issue - battery drained.
You'll likely see those threads on page 1 or 2 here for more details than this thread.
And yes 25's for them. Hopefully your work order for your battery drain mentions something besides checking battery.

Fantastic point on the OTA checks and modem power checking for it! Thank you for spelling that out. I am going to check the logs and see. Then likely turn off those nightly checks!

Didn't get a work-order, just the note below:

Unfortunately, that's all I got. The tech said "the vehicle battery monitor sensor needed to be reset." Whatever that means or does was not explained to me. Is that a process they could have done wrong? Voltages look good when fully charged on the battery so don't think the battery is my current residual issue. You very well might be right about the modem and failed coms though. You're better at troubleshooting than the dealer!

I got a follow up email from a (PCDA) Proactive Customer/Dealer Experience Specialist, - When I called he never answered or returned calls. All I got was an email that re-stating the sensor needed to be reset. He then said "Unfortunately I’m afraid that I have no available resources to assist you with this matter"

The PCDA Specialist is Travious Samuel ([email protected] Office: 1(866) 631-3788 ext. 79299)

I'm sharing contact info because I can't be the only one that has been pretty frustrated with Ford and the local dealership about these battery issues, and more people asking for help might cause resources to be allocated?

 

[HeyBales]

BMS Reset merely zero's out some tracking figures to start over on a new battery - informing system you have a new battery.
The next 9 hrs locked after that would do a BMS Relearn, for a 25MY probably learning about the state & health of the battery. For pre-25MY it has to estimate the battery specs, to then figure out the SOC & SOH.

They would have mentioned doing updates if they did it.
You should ask - since I had a 1 night battery drain and never a prior issue, don't the current SSM's regarding that apply?

The OTA aspect is just to slow your drain since it sits for awhile. Don't mention that to them - they confuse easily.

 

[rslilly76]

Ok so I had time today to check on Car scanner pro, and now I'm stumped when I click all sensors the 12v stuff is there in the BCM but car scanner pro isn't reporting anything. Maybe my cheap obd2 bt? I have the full paid version on car scanner pro too. (25 Hybrid XL fwd)

Sponsored