Strange HVB behavior

[Ranko Kohime]

2025 XLT Hybrid, FWD. I run a ScanGauge, and so I have access to the "HV State of Charge" readout from the computer.

I know all about how Li-* batteries work, and that computed SoC is only a guess, so let's get past that part.

In my Prius, (a 2017 Two-Eco with the Li-Ion pack), whatever SoC I shutdown with was what I got on startup, consistently. (I drive extensively, so greater than 1 day without driving was practically unknown to this vehicle, or my Maverick)

In my Maverick, I have observed, and tracked by conciously recording the shutdown number, a RISE in the SoC, as much as 10-15%. I am sleeping in the back seat many nights, and I typically get woken by the engine if it comes on, so it is unlikely that it is recharging the battery that way.

I have not had the problems with the 12V that others seem to, I have fuse 11 pulled, and I never connected to the Ford app, so I don't know if I'm am missing on sleep mode notifications, but my fob has worked consistently so far, excepting one event in heavy rain where the door handle would not respond. At night though, I can say with certainty that the main contactor is closing. It has a distinctive sound to my ears, that is very different from the multitude of relays clacking. I had assumed it was powering the 12V circuit for some garbage emissions reason or another, but now I am uncertain.

All this to say, I am very much unsure of my hypothesis here, but I wonder if the inverter is operating backwards, by design, or by accident, on some occasions during vehicle off time, charging the HVB from the 12V. This could be on top of any other issues, such as @Mavster Mechanic mentioned in his thread, that the 12V only charges under certain conditions when in Ready mode.

Thoughts?

Also, Ford, release the damn source code to your expensive toys. It makes it hell for us owners that we're kept in the dark about what's going in the hardware that WE OWN, and no I don't care how embarrassing the developer's comments are. #Stallman

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[Chops]

As a footnote, the OP has driven over 100,000 miles his first year. My money is on Ranko to be the first forum hybrid owner to hit 200,000. Go Ranko!!

Also 99.9% chance he did NOT get recall 26S36

 

[HeyBales]

There is a misunderstanding of what Mavster said for one thing.

Not correct that it ONLY charges the 12VB when doing the things listed.

Correct that it only keeps charging above 92 or 85% SOC (AGM or SLA) when you do those things.

Just as there is barely a bit of usage to the HVB to charge the 12VB - you'd drain the 12VB attempting to charge a tidbit of the HVB.

Grief - 12VB will drain just leaving it in Accessory only mode with radio going, lights on, ect.
Truck will turn it's self off in short order.
It's why if the HVB drops to 30% and you are in neutral mode, or key to On not started, it'll stop charging the 12VB and now the 12V system is powered by the 12VB.

As to what initiated this thinking - yes correct that ANY SOC% while a battery is being charged or discharged is a totally calculated value - known size, amps in and out, tracks it.
That can be inaccurate while it's going. Better for lithium.

True up over night. Temps make a difference. Yours goes up. It appears.
Even more so with 12VB SOC%.
Especially on pre-25MY hybrid where the battery size is not stated in BMS specs, but a learn process.

And ya if it's shutdown - it ain't turning the ICE to recharge the HVB.
Sure you turned it off? May be pretty zonked in back seat sometimes!

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