Replacing the Hybrid's OEM 12v. Battery

[Matso]

It certainly is possible for any battery to be bad off the shelf, but after 3 days of testing I would think that would already be determined. It has not. The SOC was measured through the telematics while on the phone with a service advisor. The voltage readings I measured myself at the battery terminals. A parasitic draw would be the logical culprit but that test was performed early on in this turkey shoot and nothing was found.

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[HeyBales]

It certainly is possible for any battery to be bad off the shelf, but after 3 days of testing I would think that would already be determined. It has not. The SOC was measured through the telematics while on the phone with a service advisor. The voltage readings I measured myself at the battery terminals. A parasitic draw would be the logical culprit but that test was performed early on in this turkey shoot and nothing was found.

There was another thread where poster's issue was basically false deep sleep mode activations - in that case battery was newish/recharged/tested fine - and the work order mentioned the TCU maintained it's own value for SOC%, to decide when to turn off modem after sending up the warning for Fordpass.
But it was wrong, a stuck value, other PID with SOC% reading was the expected (but poor) level that would allow remote access to work.
They ran TCU update to get past that, unless that phrasing meant telling it to update to current values, not a real software update.

Anyway - your SOC obviously SUCs merely based on voltage - but 17% seemed so low caught my eye. Normally that's the level of them agreeing bad battery.
Just to keep in back of mind.

Oh - did the ACCM update happen?

 

[Dad]

UPDATE as of 09/10/25:

Still going strong? No need to update BCM with Forescan when switching to AGM?

'23 hybrid first deep sleep message lol

Will pull the trigger on this AGM battery if all has been well.

Thanks!

Absolutely no issues since install. No need to update BCM. No "deep sleep" issues. Interior lights come on as needed. Touch door lock/unlock work flawlessly. The best upgrade I've done.

 

[Matso]

Yes, (SSM 53801) ACCM update was completed. At least according to one of the service advisors. It wasn't specified in the invoice. I should ask for verification.

 

[ScottyC]

• 10mm socket (this will fit the nut holding the cable clamps on the terminals)

When you are doing any kind of maintenance or repair of your favorite ride and find that you need a 10 mm socket...

 

[Maverick123]

This has probably been explained to death elsewhere, but I haven't found it and I'm trying to understand what's going on here. AFAIK the hybrid's gas engine is started by the HVB through one of the electric motors in the e-CVT? I'm trying to understand why a dead 12v battery prevents the truck from starting, and if / how it's possible to jump-start a hybrid if the 12v isn't what starts the engine?

Also, doesn't the HVB recharge the 12v as needed? Maybe that's the issue here, the HVB drains itself trying to keep the 12v battery charged and then doesn't have the reserve to start the ICE?

I'd appreciate a quick explanation, or a link to a thread that covers it. TIA!

 

[BlueSpec1]

When 12V battery gets flakey it can affect proper operation of modules and besides not starting can cause odd errors.

Electric Powertrain Control - Overview

Overview
The center of the electric motor control system is a microprocessor called the Inverter System Controller (ISC), also known as the SOBDMC .

The Inverter System Controller (ISC) receives inputs from sensors and other electronic components.
Based on information received and programmed into its memory, the Inverter System Controller (ISC) generates output signals to control various relays, solenoids, and actuators.

The Inverter System Controller (ISC) can only power-up if an external signal is received from the BCM, the BCMC the DCDC, the BECM, the GWM or the ECM .

There are three circuits that will wake up the Inverter System Controller (ISC): ISP-R from the BCMC , wake-up circuit from the BCM and the HEV Wake-up circuit from other HEV unique modules.

The Inverter System Controller (ISC) will not be able to wake if the Vehicle Battery Power (VBPWR) circuit from the 12V battery is not connected to the module and the module ground wire(s) are not connected.

Applying any of the 3 wake signals will cause the Inverter System Controller (ISC) to close the power relay integral to the BCMC VPWR circuits which supply main 12V power to the Inverter System Controller (ISC) and several other components.

Once the Inverter System Controller (ISC) is awake, it can sustain its own 12V power through a relay.

The ISC/ SOBDMC provides a wake up signal to the DCDC during key on.

The DCDC is responsible for maintaining and charging the 12-volt battery. The ISC/ SOBDMC sends a HEV wakeup signal to the DCDC through a hardwired circuit.

Component Description
Inverter System Controller (ISC)
The Inverter System Controller (ISC) is a stand alone module.
The Inverter System Controller (ISC) receives a variety of CAN messages and hardwired signals from modules connected to the CAN.
Based on information received, the Inverter System Controller (ISC) makes a decision on how to control the operation of the electric motor.

The high-voltage system consists of the following components:
• High-voltage battery cable
• Inverter System Controller (ISC) also known as the SOBDMC
• Electronically Controlled Continuously Variable Transmission (eCVT)
• Direct Current/Direct Current (DC/DC) converter control module
• ACCM and A/C compressor assembly located on lower LH side of the engine block
• High voltage battery pack

 

[Tyler]

This has probably been explained to death elsewhere, but I haven't found it and I'm trying to understand what's going on here. AFAIK the hybrid's gas engine is started by the HVB through one of the electric motors in the e-CVT? I'm trying to understand why a dead 12v battery prevents the truck from starting, and if / how it's possible to jump-start a hybrid if the 12v isn't what starts the engine?

Also, doesn't the HVB recharge the 12v as needed? Maybe that's the issue here, the HVB drains itself trying to keep the 12v battery charged and then doesn't have the reserve to start the ICE?

I'd appreciate a quick explanation, or a link to a thread that covers it. TIA!

The "quick" explanation is that the truck computer(s) (BCM, ECU, etc) control the HVB, and the 12V battery powers the truck computer(s). That is to say, if your 12V system goes down, the HVB is too "dumb" to do anything on its own.

Most Hybrids / EV / Alternative fuel vehicles still use a 12v system as their "control" power.

 

[Maverick123]

The "quick" explanation is that the truck computer(s) (BCM, ECU, etc) control the HVB, and the 12V battery powers the truck computer(s). That is to say, if your 12V system goes down, the HVB is too "dumb" to do anything on its own.

Most Hybrids / EV / Alternative fuel vehicles still use a 12v system as their "control" power.

Thanks to you and @BlueSpec1 for the explanations, I sort of understand it now. When you "jump start" a hybrid, you aren't actually sending power to the starter; you're only powering up the Vehicle Battery Power (VBPWR) to give the ISC the 12v wake signal so it can make the HVB start the engine. PS: What happens if the car's been sitting forever and the HVB is drained?

"The Inverter System Controller (ISC) will not be able to wake if the Vehicle Battery Power (VBPWR) circuit from the 12V battery is not connected to the module and the module ground wire(s) are not connected.

Applying any of the 3 wake signals will cause the Inverter System Controller (ISC) to close the power relay integral to the BCMC VPWR circuits which supply main 12V power to the Inverter System Controller (ISC) and several other components.

Once the Inverter System Controller (ISC) is awake, it can sustain its own 12V power through a relay."

 

[Dad]

Just for later readers of this thread.

No - the OEM battery on the 22-24's hybrids (which this whole thread is about) was NOT an AGM battery.

The OEM battery on the 25 hybrids is AGM.

The OEM battery on majority of 22-24 EB's was AGM, and a recall to replace the ones that got FLA happened.

The points about Amazon is the fact it won't think the listed AGM battery which is the correct size to replace the OEM one, is correct. Because OEM was not AGM.

Thanks for re-clarifying this for later readers.

 

[Dad]

So what is the battery size in the 2025's?

I believe it's the same size as previous years; Size H4. I don't think Ford changed the battery size for the 2025 hybrids.

 

[Dad]

Following AGM installation on my hybrid, the deep sleep mode continues and the voltage drops to around 11.7 every morning. The latest SOC was 17%. It's once again back in the service department for the 5th time. They will probably keep it all week and in the end I have doubts they will find the problem. But they sure are trying. It's almost time to squeeze the sour juice out of this one. Sad.

I'm thinking either a dysfunctional AGM battery or it's something that is giving false information to the truck's computer.

 

[Dad]

But the OEM battery was an AGM battery. Amazon just doesn't distinguish between hybrid and ICE for battery selection.

I think this was answered in another post, but since you're asking me directly, I'll take the liberty of repeating. The OEM in all Mavericks prior to 25, is a flooded lead acid battery, not an AGM battery. Amazon did not "approve" of the AGM replacement because it wasn't an OEM item and no doubt Amazon did not want to venture into any liability issues that might emerge. Rest assured the size H4 AGM battery will fit the Maverick without any modification or reset.

 

[MakinDoForNow]

I think this was answered in another post, but since you're asking me directly, I'll take the liberty of repeating. The OEM in all Mavericks prior to 25, is a flooded lead acid battery, not an AGM battery. Amazon did not "approve" of the AGM replacement because it wasn't an OEM item and no doubt Amazon did not want to venture into any liability issues that might emerge. Rest assured the size H4 AGM battery will fit the Maverick without any modification or reset.

My 2023 Tremor 2.0 came with an AGM. The 2022-2023 at least came with a group 99 which is 5/8"-3/4" shorter than an H4. The blue and white (stand in?) labeled ones may have been a regular H4 or a group 99. I don't know as my 3 hybrids all came with the 390cca BXT99RTA. The taller H4 size would just not have as much clear airspace as the group 99, if it would matter or not with heat buildup.

 

[BlueSpec1]

PS: What happens if the car's been sitting forever and the HVB is drained?

Long storage has been mentioned a couple of times, most recently in:
https://www.mavericktruckclub.com/f...age-6-months-effect-on-hvb.71334/post-1180696

The service manual mentions low HVB SOC.

The 12V battery is usually the one I've focused on.
I have looked at the HVB SOC a couple of different times, it's always changing during normal use.

Feb 2024: 60.98%

April 2024: 38.52%

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