Hybrid: which battery powers which systems? Is there a list?

[doug maverick]

Is there a list of what each of the two batteries in the Hybrid powers?

what powers interior lights?
which actually powers the engine starter?
what charges the 12V battery located under the rear seat?
what powers the wipers, a/c fan, washer fluid... turn signals...

and so forth.

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[DWV]

In basic and simple terms, the HV battery drives the transmission when in "electric", charges the 12 v battery, and starts the gas engine.

The 12v battery does the rest, including waking up the HV battery to start the engine.

If the 12v battery is dead, nothing works.

 

[StarBug]

And to be clear the electric motors are always on, even if the ICE is running the motors are required to spin to provide the correct gear ratio, so there isn’t really a “non-electric” mode in a hybrid, just an “also gasoline” mode.

 

[Hcopter]

Here's the reply from Grok when asked your question. I agree with it except where it says the HV battery is ~450V, from what I've read and from my Car Scanner app it's ~250V.

------------------------------------------------

Devices/Systems Primarily Powered by the High-Voltage (HV) Battery

The HV battery drives the electric side of the powertrain and high-power components (often via electric motors or inverters). Key items include:

• Electric traction motor(s) in the eCVT transmission for propulsion assistance, electric-only driving (limited range/speed), and torque fill.
• Motor/Generator 1 (MG1): Starts the gasoline engine and generates electricity to charge the HV battery or power systems.
• Electric A/C compressor: Fully electric (no belt drive from the engine), allowing A/C to run with the engine off or in EV mode.
• Hybrid control modules and power electronics: Manage power flow between engine, motors, and battery.
• Power steering, water pump, and other "beltless" accessories (electric versions in the hybrid).

Note: The HV system uses orange high-voltage cabling and should only be serviced by trained technicians due to the ~450V potential.


Devices/Systems Primarily Powered by the 12-Volt Battery (or DC-DC Converter)

All standard vehicle accessories and low-voltage electronics run on the 12V system. The DC-DC converter from the HV battery keeps it charged while the vehicle is running.

• Lighting: Headlights, taillights, interior lights, dashboard lights.
• Infotainment and displays: Radio/audio system, touchscreen, navigation, instrument cluster.
• Climate control accessories: Blower fan, heater (defrosters), controls (compressor is HV, but fan/controls are 12V).
• Power features: Windows, door locks, mirrors, seats (if powered/heated).
• Electronics and outlets: USB ports, 12V power points, 120V inverter (if equipped, via inverter from 12V system), bed power outlets.
• Safety and control systems: ABS brakes, electronic stability control, airbags/sensors, vehicle control modules (BCM, etc.), cameras/sensors.
• Other: Horn, wipers, starter relays/contactors (to engage HV system), alarms, keyless entry.
• Engine start support: The 12V battery powers initial electronics and closes HV contactors; the actual engine cranking uses MG1 from the HV battery.

Key Notes on Operation

• When the vehicle is "on" (ready mode): The HV battery (via DC-DC) primarily sustains the 12V system. The gas engine starts as needed for charging or power.
• When off: Only the 12V battery is active for standby loads. Prolonged accessory use (e.g., lights, inverter) can drain it without the engine running.
• Inverter/120V outlets (if equipped): Powered through the 12V system/inverter, ultimately sourced from the HV battery via DC-DC.
• The HV battery does not directly power standard 12V accessories.

 

[doug maverick]

Here's the reply from Grok when asked your question. I agree with it except where it says the HV battery is ~450V, from what I've read and from my Car Scanner app it's ~250V.

------------------------------------------------

Devices/Systems Primarily Powered by the High-Voltage (HV) Battery

The HV battery drives the electric side of the powertrain and high-power components (often via electric motors or inverters). Key items include:

• Electric traction motor(s) in the eCVT transmission for propulsion assistance, electric-only driving (limited range/speed), and torque fill.
• Motor/Generator 1 (MG1): Starts the gasoline engine and generates electricity to charge the HV battery or power systems.
• Electric A/C compressor: Fully electric (no belt drive from the engine), allowing A/C to run with the engine off or in EV mode.
• Hybrid control modules and power electronics: Manage power flow between engine, motors, and battery.
• Power steering, water pump, and other "beltless" accessories (electric versions in the hybrid).

Note: The HV system uses orange high-voltage cabling and should only be serviced by trained technicians due to the ~450V potential.


Devices/Systems Primarily Powered by the 12-Volt Battery (or DC-DC Converter)

All standard vehicle accessories and low-voltage electronics run on the 12V system. The DC-DC converter from the HV battery keeps it charged while the vehicle is running.

• Lighting: Headlights, taillights, interior lights, dashboard lights.
• Infotainment and displays: Radio/audio system, touchscreen, navigation, instrument cluster.
• Climate control accessories: Blower fan, heater (defrosters), controls (compressor is HV, but fan/controls are 12V).
• Power features: Windows, door locks, mirrors, seats (if powered/heated).
• Electronics and outlets: USB ports, 12V power points, 120V inverter (if equipped, via inverter from 12V system), bed power outlets.
• Safety and control systems: ABS brakes, electronic stability control, airbags/sensors, vehicle control modules (BCM, etc.), cameras/sensors.
• Other: Horn, wipers, starter relays/contactors (to engage HV system), alarms, keyless entry.
• Engine start support: The 12V battery powers initial electronics and closes HV contactors; the actual engine cranking uses MG1 from the HV battery.

Key Notes on Operation

• When the vehicle is "on" (ready mode): The HV battery (via DC-DC) primarily sustains the 12V system. The gas engine starts as needed for charging or power.
• When off: Only the 12V battery is active for standby loads. Prolonged accessory use (e.g., lights, inverter) can drain it without the engine running.
• Inverter/120V outlets (if equipped): Powered through the 12V system/inverter, ultimately sourced from the HV battery via DC-DC.
• The HV battery does not directly power standard 12V accessories.

exactly what I was looking for.

 

[HeyBales]

12VB powers the 12V system (everything that may turn on) - if the truck is off or key is in Accessory position (for push button start - you don't get this mode truly it appears, without a bunch of things done just right).

HVB powers nothing until truck hits On or Started. Which the 12VB throws the relay to allow that.
Then HVB powers the 12V system thrue DCDC.

At that point the 12VB is merely the receiver of juice like anything else from the DCDC Converter on the 12V system.

Grok was good info - some prior posts misunderstood stuff.

Even some momentary disconnects of the 12V battery (just discovered this) do not throw the relay for the HVB off, eventually it will though.
So when in On state, drops to Accessory.
When Running but not moving, drops to Accessory.
Not about to test while Running and moving. Even if I had person in backseat to do the disconnect.

 

[doug maverick]

ok, so when the Ford app say "Battery Save Mode" (BSM) it is due to the voltage at the 12V, or a combination of the voltages from both HVB and 12V?

My truck went into BSM yesterday when I was doing a bunch of stuff inside the cabin, and doors were open and closed started it about 6 times without driving, etc. Probably used a few amps all together. So I charged the 12V using a smart 3 stage charger for a few hours. As soon as I disconnect the charger, the battery showed 13.4v, and this morning after sitting all night, was at 12.4v (I did not lock the doors) 12.4v isn't dead, but probably about 60% charged?

At one point today, I had full access with the Ford app, then it dropped back to BSM.

I've poured over a bunch of DSM and saver mode thread here, and have figured out that its a very complicated subject why these trucks go to saver mode.

I know this is the original factory battery in the truck because I bought it from original owner, and he says it's the one that came new. I've already ordered a new AGM H4 for the truck. Maybe that will be the answer?

Thanks to all of you for your input and comments.

 

[Hcopter]

ok, so when the Ford app say "Battery Save Mode" (BSM) it is due to the voltage at the 12V, or a combination of the voltages from both HVB and 12V?

BSM is only related to the 12V battery.

 

[A112358]

Noob question: Is this right, with the hybrid engine, there is no traditional alternator, the 12V battery gets its recharge from the hybrid battery system?

 

[Mavster Mechanic]

Noob question: Is this right, with the hybrid engine, there is no traditional alternator, the 12V battery gets its recharge from the hybrid battery system?

Yes.

But in a round about way.

The gas engine spins a REALLY LARGE alternator that makes high voltage that recharges the high voltage battery.

The High Voltage Hybrid Battery connects to a step down DC/DC converter that pretends it's an old fashioned alternator/generator by outputting a variable 12.5v to 15.5v.

The computer software a lot of people complain about lowers the voltage too soon which essentially stops charging too soon, but is enough to power all your 12 volt devices. You should never get a dead battery on the road. But you can if it sits too long because chances are it was not fully charged at the time you parked it.

Length of drives past 45 minute usually don't help. Usually it stops charging between 45 and 60 minutes into a drive. But short trips make if worse. Unless you drive af night.

 

[A112358]

Yes.

But in a round about way.

The gas engine spins a REALLY LARGE alternator that makes high voltage that recharges the high voltage battery.

The High Voltage Hybrid Battery connects to a step down DC/DC converter that pretends it's an old fashioned alternator/generator by outputting a variable 12.5v to 15.5v.

The computer software a lot of people complain about lowers the voltage too soon which essentially stops charging, but is enough to power all your 12 volt devices.

Great explanation. Thanks.

 

[doug maverick]

But short trips make if worse. Unless you drive af night.

My normal driving habit is trips of about 8-12 miles miles each in daytime, sometimes only one per day. I might drive at night a few times per month.

What is the best strategy for my situation to avoid a dead battery? I don't use Forscan, and would rather not go that route.

 

[Suzukiridr14]

In basic and simple terms, the HV battery drives the transmission when in "electric", charges the 12 v battery, and starts the gas engine.

The 12v battery does the rest, including waking up the HV battery to start the engine.

If the 12v battery is dead, nothing works.

Exactly, and to the point!

 

[Mavster Mechanic]

My normal driving habit is trips of about 8-12 miles miles each in daytime, sometimes only one per day. I might drive at night a few times per month.

What is the best strategy for my situation to avoid a dead battery? I don't use Forscan, and would rather not go that route.

If you start out with a new/good/normal/fully charged 12v battery, then

IT SEEMS / THERE IS EVIDENCE that running your headlamps all the time will "nudge" the computer into doing a better job of charging the 12v battery.

Has to be full headlamps (and tail lamps). Daytime running lights are not effective.

It's worked for me for 2 weeks, but it's only been 2 weeks.

More owners doing this experiment will help confirm it.

It may not revive an already weak / sulfated battery.

 

[SafetyGuy]

My normal driving habit is trips of about 8-12 miles miles each in daytime, sometimes only one per day. I might drive at night a few times per month.

What is the best strategy for my situation to avoid a dead battery? I don't use Forscan, and would rather not go that route.

Good question.

Lots, lots and lots of threads on this and can be mind boggling going through them all.

As a Hybrid Maverick owner, this is my short list for battery maintenance.

-Charge 12 volt Battery completely,
-Carry out a battery relearn where the truck learns that your battery is full and to start charging it to the new level...may take a few trys to get it to stick, and a variance from the manual ia to let the truck sit for 10 hours locked and closed up with no charger attached,
-When driving, even in the daytime, turn your headlights ON!

This seems to HELP put a load on the 12 volt system and truck then charges battery better.
-
I have added a good thread to start reading on a recent conclusion put forward about this from @Mavster Mechanic .

Andy

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