HYBRID 12V Battery Mystery SOLVED

[Mavster Mechanic]

Above 12.6 volts in the morning is normal. 12.8 is awesome and what you may see from a new battery.

In enough time I'll figure out if headlamp every drive is needed, or if 1 hour of headlamps per week is just as good.

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[Ryom]

2025 Hybrid Lariat on this morning's drive, I remote start and idle for 15 mins before leaving. Heated seats and steering wheel used in the colder months. Headlights on automatic.

Cell phone and dash cam plugged into front USB and lithium jump pack in the rear. No other accessories.

No battery issues so far. It sat at the body shop for about 2 weeks last year and started right up afterward.

Below is ACC only 12 hours later...

And then ACC off prior to opening the door...

 

[Mavster Mechanic]

2025 Hybrid Lariat on this morning's drive, I remote start and idle for 15 mins before leaving. Heated seats and steering wheel used in the colder months. Headlights on automatic.

Cell phone and lithium jump pack plugged into front and rear USB. No other accessories.

No battery issues so far. It sat at the body shop for about 2 weeks last year and started right up afterward.

Below is ACC only 12 hours later...

And then ACC off prior to opening the door...

Your battery may last 3 years like that. But already it is showing signs it has some sulfation going on.

Above 15v is like "it knows it's underperforming and it is trying to hurry up and play catchup" on the charging. In a 2022 a healthy battery charges at 14.7 to 14.8. Just like most textbooks say you should do.

May sound like splitting hairs. And maybe it is. But these are the subtle symptoms. Which is why most dealers / mechanics say it's fine like that. And it kind if is fine like that for long time. Just life shortening (for the battery).

Just coming off a drive 12.2 is kind of low but adequate to get you by for a long time.

 

[Mavster Mechanic]

It is commonly stated sulfation starts at 12.4 volts and below.

It is commonly stated Flooded Lead Acid can withstand up to 16.0 volts.

It is commonly stated AGM batteries should not exceed 15.0 volts.

AGM therefore should never be put on the repair / desulfate cycle of some chargers so equipped. 16 volts is the common voltage used to attempt to dissolve lead sulfate crystals.

 

[Bluebeard22]

It is commonly stated sulfation starts at 12.4 volts and below.

It is commonly stated Flooded Lead Acid can withstand up to 16.0 volts.

It is commonly stated AGM batteries should not exceed 15.0 volts.

AGM therefore should never be put on the repair / desulfate cycle of some chargers so equipped. 16 volts is the common voltage used to attempt to dissolve lead sulfate crystals.

Some of you will laugh.
Some of you will cry.
Some of you will say "Holy Crap that's amazing!"
Some of you will say "Holy Crap that's dumb."

Here goes.

Fact: 2022 Hybrid (and others) actively drain a 12 volt battery to the computed 80% charge level.
Then do not try to add charge to the 12 volt battery until a computed 60% or lower charge is reached. God only knows why.
For 3.5 years my 12v battery has been "maintained" at about 60% charged. Always a resting voltage of 12.1 or 12.2.

Fact: running your headlamps will force the 12v battery to be 100% charged given enough time. (DRL will not do it. Parking Lamps only will do it.)

Fact: running your vents blower at speed 6 or 7 will force the 12v battery to be charged to 100% given enough time.

Fact: attaching a trailer, 4-pin or 7-pin will force charge the 12v battery to 100%.

Theory A: the truck needed to detect 12 volt demand, and above a certain wattage to trigger 12 volt charging.

Why would fan level 6 trigger battery recharging and fan level 5 would not? Why would full headlamps trigger battery recharging, but DRL would not?
Did the truck detect demand to run my camper fridge and coach battery?

I tested this last part. From Amazon I ordered a $10 LED brake light for the 2" hitch receiver with 4-pin connector.
Wow! The LED brake light pulling no power when not braking, and only 4 or 5 watts when braking DOES TRIGGER 12 volt battery recharging to 100%.
It's not the electrical demand that triggers recharging. It is simply thinking a trailer is there that triggers recharging.

Theory A shot down.

But this explains a lot.
This explains why some people have more 12v battery issues than others.

Those that drive at night a lot have more battery charging by happenstance.

Those that use fan speed 6 or 7 have more battery charging by happenstance.

Those who connect trailer wiring (and you don't even need a trailer!) have more battery charging.

Not a permanent fix. But a work around. Some of you may prefer running your headlamps more often over plugging into a home charger.

My 12v battery has been 100% for ten days in a row now. And is maintained at 12.7 or 12.8 volts. But I need to do one of the three "triggers" above or it rapidly starts to decline.

More to come...

I just got the dreaded deep sleep message (parked at the airport for. Week). I would be interesting to know if having the climate control fan speed set at auto 3 would achieve the same as having you fan speed set to 6 or 7.

 

[Mavster Mechanic]

I just got the dreaded deep sleep message (parked at the airport for. Week). I would be interesting to know if having the climate control fan speed set at auto 3 would achieve the same as having you fan speed set to 6 or 7.

No. Not the same.

And deep sleep is not a bad thing.
This is a GOOD THING when you are parked at airports. Deep Sleep is what allowed you to drive home from the airport.
Without deep sleep you might have had to call a tow truck.

 

[MakinDoForNow]

It is commonly stated sulfation starts at 12.4 volts and below.

It is commonly stated Flooded Lead Acid can withstand up to 16.0 volts.

It is commonly stated AGM batteries should not exceed 15.0 volts.

AGM therefore should never be put on the repair / desulfate cycle of some chargers so equipped. 16 volts is the common voltage used to attempt to dissolve lead sulfate crystals.

Noco G series (maybe others?) have battery type specific setting. My G10 will take my 200ah 6volt agm batteries to 7.3v during optimization cycle & after completion for 24 hours batteries will settle to 6.4volts. The Noco has a "REPAIR" cycle which requires removal of battery from the vehicle to protect vehicle from "possible damage".

 

[HeyBales]

2025 Hybrid Lariat on this morning's drive, I remote start and idle for 15 mins before leaving. Heated seats and steering wheel used in the colder months. Headlights on automatic.

Cell phone and dash cam plugged into front USB and lithium jump pack in the rear. No other accessories.

No battery issues so far. It sat at the body shop for about 2 weeks last year and started right up afterward.

Below is ACC only 12 hours later...

And then ACC off prior to opening the door...

Your 1st ACC only pic showing 14.5 proves it was not ACC only.
Push button start you can't get into ACC only easily, but you showed how to do it - on turnoff.
Of course that's an inflated reading after it's been charging, as commented not too healthy either.
My battery at 11.8V (11.9 this morning!) morning resting is usually 12.1 to 12.3 after a drive.
I'm surprised your AGM is at that point already.
I'm not surprised the 25MY doesn't appear to have changed BMS strategy.

Another thread someone posted the convoluted steps to get a morning resting voltage reading.
Push button On with no brake pedal.
That throws the relay for the HVB and now 12VB charging at very high amps.
Immediately button Off to stop that (or learn how long a pause you need), and now you can hit the brights for a few seconds to drop the surface charge from what just happened.
That will give you a more legit resting voltage reading.
Maybe every few days do the routine to see.

 

[Finnster]

2025 Hybrid Lariat on this morning's drive, I remote start and idle for 15 mins before leaving. Heated seats and steering wheel used in the colder months. Headlights on automatic.

Cell phone and dash cam plugged into front USB and lithium jump pack in the rear. No other accessories.

No battery issues so far. It sat at the body shop for about 2 weeks last year and started right up afterward.

Below is ACC only 12 hours later...

And then ACC off prior to opening the door...

Thanks for posting about what I believe will be the MY25(and possibly MY26) version of MY22-24 12V battery undercharging issue!
The difference that I am seeing is that some or all of the MY25's are constantly overcharging their 12V AGM hybrid batteries!

My personal 2025 hybrid has done this from day one! Recharging the 12V battery with a Noco 1 charger refreshes the battery, but not for long.
At some point we should start a separate thread on this apparently different issue.

 

[HeyBales]

I just got the dreaded deep sleep message (parked at the airport for. Week). I would be interesting to know if having the climate control fan speed set at auto 3 would achieve the same as having you fan speed set to 6 or 7.

If only a week - you didn't get that action because of 14 days non-start then.
Likely the SOC below 40% reason.
Unless voltage really dropped to 9.5V.

But SOC close enough to 40% that a week dropped it below that - I'd bet your battery is too far gone for this method to have a positive effect.
Got a powerport voltage reading?
I'm doubting you ever see it below 14V while running.
My 24MY with 11.8V normal and 50-60% SOC - no change to amps with this method.

 

[Mavster Mechanic]

Noco G series (maybe others?) have battery type specific setting. My G10 will take my 200ah 6volt agm batteries to 7.3v during optimization cycle & after completion for 24 hours batteries will settle to 6.4volts. The Noco has a "REPAIR" cycle which requires removal of battery from the vehicle to protect vehicle from "possible damage".

NOCO 5 Genius has a repair mode.

Does not say it is good for AGM. So you'll need a volt meter at the same time to check on it.

 

[MakinDoForNow]

Your 1st ACC only pic showing 14.5 proves it was not ACC only.
Push button start you can't get into ACC only easily, but you showed how to do it - on turnoff.
Of course that's an inflated reading after it's been charging, as commented not too healthy either.
My battery at 11.8V (11.9 this morning!) morning resting is usually 12.1 to 12.3 after a drive.
I'm surprised your AGM is at that point already.
I'm not surprised the 25MY doesn't appear to have changed BMS strategy.

Another thread someone posted the convoluted steps to get a morning resting voltage reading.
Push button On with no brake pedal.
That throws the relay for the HVB and now 12VB charging at very high amps.
Immediately button Off to stop that (or learn how long a pause you need), and now you can hit the brights for a few seconds to drop the surface charge from what just happened.
That will give you a more legit resting voltage reading.
Maybe every few days do the routine to see.

When first getting into push button start insert the voltage display into the cig power port then look at it and push the push start without foot on brake. The 12v reading will be displayed for 0.5-0.7 seconds before the relay activates the HVB charging. Though this reading may be reduced 0.1v (+/-) for other active draws on the buss. There could also be a slight reduction in reading in the stated reading after bleeding off the surface charge if anything else remains active. Have to take readings at battery post maybe.

 

[Jeffs72MGB]

I'm in your boat. FORScan only runs on Windows (there's an iOS version, but it's only diagnostic). I don't have a Windows computer. I borrowed my brother-in-law's, but it would shut down intermittently . . . worse than useless. Still looking to borrow one. Someone needs to tell the FORScan people there's another computer platform in the marketplace. Sheesh.

A Mac can run Windows but a PC can't run Mac. You need to portion your hard drive and use Bootcamp. I do this and it works great.

 

[Ryom]

Maybe we should keep an eye on the sodium battery thread too, if Ford doesn't solve the BMS issues it may be the most durable option

 

[Dad]

A Mac can run Windows but a PC can't run Mac. You need to portion your hard drive and use Bootcamp. I do this and it works great.

You're correct, and thanks for the reminder. BootCamp works on older Macs. For newer Macs (Silicon processor), Parallels. The problem is financial; while Bootcamp comes with the Mac, Parallels is about $80. In addition, one has to purchase the Windows OS. Much cheaper than buying a new PC, but less than just borrowing one for a day.

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