HYBRID 12V Battery Mystery SOLVED

[rslilly76]

I'm not sure that leaving the truck on while you're not in it will add any charge. This morning I got out and left it running with the headlights on, and locked the door. The voltage dropped to 12.8v and stayed there until I got back in and closed the door, and it went back up to 14.4v.

this was with the door wide open in my driveway running

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[Finnster]

@rslilly76,
How many miles are on your 2025 XL hybrid?

 

[rslilly76]

@rslilly76,
How many miles are on your 2025 XL hybrid?

17,414 according to Ford Pass

 

[ryan2366]

Yes you can with Forscan. You change it from the default "Auto" setting to "Last Known" position. I did this on my 25MY Hybrid. So if you turn Mav off with headlights in Headlight position, the switch will be in that position when you turn truck on. It's Fortran setting Ez BCM Autolock Initial Value, or 726-27-03 XXXX-XX3X-XXXX (7th hex # set to 3).

I fully realize I'm reading the DC-DC converter voltage. I'm just submitting my Mav behavior vs some where this running voltage drops while ON, obviously indicating . And hopefully we all realize the charging mechanism is active when the truck is ON, Rotary Dial even in Park, Drive models optional. Thanks for your hard work on all our behalf. Very educational.

I’m not sure what I was doing wrong but I tried the last known setting.

When I shut the vehicle off my headlights remain on and I have to turn them off manually.

After 45 minutes of changing settings and testing both in park and drive, I ended up putting tape over the dashboard light sensor to achieve headlights on all the time.

Maybe Canadian DRL settings are preventing the last known setting of headlights on???

 

[HeyBales]

If you have the headlights off, and you have the a/c off, and radio off what exactly is there left to power?

Every module that allows the truck to operate.
There are many.

 

[HeyBales]

I'm not sure that leaving the truck on while you're not in it will add any charge. This morning I got out and left it running with the headlights on, and locked the door. The voltage dropped to 12.8v and stayed there until I got back in and closed the door, and it went back up to 14.4v.

Was the door locked a difference?

We've had 1 poster that charged up his battery at work leaving it running and locked until lunch, while he worked.

Now - this was prior to this thread's info - he was merely going for the long float charge below 1A that happens normally.
And since his battery was not 100% already or close - it never dropped to that 12.8 V reading.
So could be a difference.

But I bet door locked is too.
If you test by getting in it and locking door - lock the same method.
If by door, or by fob.
Makes a difference with alarm activated.

 

[HeyBales]

Wonder if the voltmeter phone charger is enough to trigger the BMS to charge to 100% too? MMMM

I'm not going to find the post - already tested - nope.

 

[rslilly76]

I'm not going to find the post - already tested - nope.

then explain why my battery is charging with all the other stuff off?

 

[Mavster Mechanic]

Wonder if the voltmeter phone charger is enough to trigger the BMS to charge to 100% too? MMMM

No

 

[rslilly76]

No

 

[Mavster Mechanic]

then explain why my battery is charging with all the other stuff off?

How do you know it is?

Have you connected an ammeter?

 

[rslilly76]

How do you know it is?

Have you connected an ammeter?

 

[HeyBales]

OK well I am curious if Ford has done some sort of software upgrade to fix this on the 25+ and here are my reasons for that. I had all software updates done (12 total a month after getting the truck in April of 25, the truck was built in Jan of 25) including the ACCM for the a/c that is supposedly a fix lol. I also have an AGM cause it's a 25 so it came with one.

At rest I am 12.9 volts
With key in the on position (not running) I am at 13.0 volts
With the Truck on (no lights on, no radio on, no A/C on, nothing connected to trailer light plug) 14.2 volts

Voltmeter connected directly to the 12v battery shows 14.37 volts which would indicate it's being charged at the current time.

I don't have the same program that the mechanic has, so I can't seem to find a way to verify what state of charge my 12v is in at the moment. (Does anyone know if Car Scanner Pro will show the 12v state of charge?)

Be aware this BMS and DCDC method can allow those Volts but very little Amps to be sent to the battery. Like picture below - which was shortly going to drop to 14.8V and 0.2A.

As soon as you go to On state with push button start (which yours does with On button and no brake) - the 12V battery has thrown the relay - and the HVB and DCDC is all online now - so battery charging state. Only difference with running, is when the HVB gets to 30%, the engine will turn on. If just On state, at some point the charging stops to prevent draining the HVB.

Car Scanner does show the extra info, just not broken out per module like Forscan Lite is, might have to dig more. Here are the PID names though. So BCM, not BECM. Pick Batt_Curr_2 if able, you get finer reading.

 

[Hcopter]

this was with the door wide open in my driveway running

I'm not sure if the 2025 is different, but your state of charge (SOC) is probably below 85%, in which case the voltage will stay at 14.X when the truck is on, regardless of doors, lights, etc. However, once the SOC is above 85% the voltage will drop to about 12.8 unless you turn on the lights, fan, etc., that's when opening the door starts having an effect on the voltage.

Car Scanner does have a 12v SOC reading, that's what I'm using.

 

[rslilly76]

Be aware this BMS and DCDC method can allow those Volts but very little Amps to be sent to the battery. Like picture below - which was shortly going to drop to 14.8V and 0.2A.

As soon as you go to On state with push button start (which yours does with On button and no brake) - the 12V battery has thrown the relay - and the HVB and DCDC is all online now - so battery charging state. Only difference with running, is when the HVB gets to 30%, the engine will turn on. If just On state, at some point the charging stops to prevent draining the HVB.

Car Scanner does show the extra info, just not broken out per module like Forscan Lite is, might have to dig more. Here are the PID names though. So BCM, not BECM. Pick Batt_Curr_2 if able, you get finer reading.

so this is forscan lite on your phone? I asked what program everyone is using you're the first to respond

also mine in hybrid XL no push button is keyed ignition

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