Battery percent increasing after unplugging

[AScaLightning]

Hi all, in the last couple of weeks this is the scenario I’m seeing. Any ideas?

1. Battery on L2 charger overnight set to end at 85%
2. Battery indicator shows charged to 85, unplug, and start driving
3. Within a mile my battery percentage increase 2%

This scenario occurs whether I set the charge to end at 70, 80, 85, 90…

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[Tom M]

I often experience this. I attribute this to the battery warming up slightly after staring the trip. It is usually 1-2% for me. Alternatively: I may be due to regenerative braking.

 

[chriserx]

I often experience this. I attribute this to the battery warming up slightly after staring the trip. It is usually 1-2% for me.

In minnesota this is highly likely. Set it to 100% and see if you get 102%, or to balance cells. w/e.

 

[shutterbug]

Hi all, in the last couple of weeks this is the scenario I’m seeing. Any ideas?

1. Battery on L2 charger overnight set to end at 85%
2. Battery indicator shows charged to 85, unplug, and start driving
3. Within a mile my battery percentage increase 2%

This scenario occurs whether I set the charge to end at 70, 80, 85, 90…

Happens to me every day. Even if I neglected to charge overnight. I don't worry about that.

 

[TaxmanHog]

Since you were still on the plug during the morning remote start or departure conditioning, a small amount of extra energy might make it to the HVB while the EVSE is trying to 'sustain' energy for the heating process.

 

[AScaLightning]

Thanks for responses everybody. I hadn’t noticed it prior to this - but maybe I wasn’t looking…. Good to know it isn’t a sign of something going wrong. I love the truck and will drive it as long as possible.

 

[RST]

Mine has been doing the same thing as of late, and it is a new behavior. On my 3rd winter with this truck, never did this before, so don't think it's anything to do with warming batteries. Haven't received an update since 9/19, so that's not it either. I'm stumped.

 

[garsh]

The BMS (Battery Management System) is what attempts to measure the battery's state. It is not perfect. It's difficult to measure chemical potential energy. Especially when each of the cells that make up the battery can be at slightly different levels. There's no way to directly measure battery capacity, so the BMS will look at voltages and perform coulomb counting as the battery is used.

Changes in battery state after unplugging could be due to things like temperature changes, or the BMS performing cell balancing. But it's also possible that the BMS has simply updated its estimate.

Either way, it's nothing to worry about.

 

[fhteagle]

"BMS Sway". In my '22, I often see little 2 to 4% SOC indication swings, especially right at the start of the trip. Seems like the pattern is when it's warm out, the SOC goes up or stays up more than the consumed kWh would lead one to believe. When cold (<40F maybe), it seems to be the opposite, 100% charge limit becomes 96% indicated SOC before even a mile of driving has gone by.

 

[JRDM2]

I had experienced similar last week. I returned from a quick trip to the local grocery store with a percent higher state of charge reading than I left with. I had assumed this was because the number was an estimate instead of a precise number.

 

[Adventureboy]

This is my 4th winter with the Ligntning and this is normal in the cold. I think the BMS takes a best guess based on complex calculations with the environmental conditions and charges conservatively to SOC under those conditions. This is better (less alarming) than a drop immediately after you start. When you start the truck, it starts warming the battery and it seems it adjusts to account for its conservative approach to charging to SOC. I think it simply comes down to the accuracy of managing all of the input parameters. I actually prefer it this way. I charge to 85%, and a mile down the road, I have 87% and feel good about that.

I find it most noticeable around the freezing mark where the BMS is managing a number of additional variables to keep the battery in the green temperature zone.

 

[WXman]

Yep mine too is wacky. I charge to 95%. By the time I've driven 2 miles I'm at 98%. This week I drove to work 19 miles through two cities with a stretch of highway in between and was still at 93% when I arrived. But then in the afternoon when I drive back home my range is obliterated. I think the gauge on the dash is just very inaccurate.

 

[HornetRaider]

Mine does the same. I set it to 80% and notice it's at 81% when I'm turning out of my subdivision.

 

[Adventureboy]

when I drive back home my range is obliterated

I expect this is because the battery has cooled through the day while not plugged in, so it takes a bunch more energy on startup to warm it. Take a look at the trip details when you arrive at work, then when you arrive home. I suspect more energy is used for external temperature on the way home. External temperature might be a bit warmer, but the battery may start in a colder state on the way home.

 

[chl]

Never seen this effect with my 2023 Pro SR battery.
I set my charging to stop at 80%.
Has not gotten really cold here yet, no lower than the 30's except maybe one night it hit 28.
I keep the truck on the FCSP (L2) when the temp gets into the 40's but it doesn't use very much energy for warming most of the time does not even register in the "Insights" screen.

So if it were a large difference or a large drop in SOC, I'd say there could be bad cells in the battery.

A small change like this is likely just the battery warming up when you turn the truck on and head out - the voltage will rise when the battery gets warmer (the internal resistance falls) and I believe the SOC number is based on the terminal voltage along with coulomb counting where the measured current is integrated wrt time during charging and discharging.

But the Ford algorithm details have not been published as far as I know.

So, my theory:

You are charging in cold weather so the battery is cold, the resistance is higher when cold so the terminal voltage is lower, coulomb counting is primarily used to determine how much energy has been added to the battery and the battery voltage is used to adjust that number (with their algorithm) and then when the number matches your set point for SOC the charging stops.

Then later you start your truck and start driving drawing energy from the battery, the battery warms up, that then raises the terminal voltage and the measured terminal voltage adjusts the previous number determined by coulomb counting when the battery was cold upwards as a result.

The adjustments you are seeing are small so they are likely just based on the battery voltage changes when cold vs warm changing the SOC number calculated by coulomb counting.

One has to remember that these SOCs are calculated estimates of the energy stored in the battery, the calculations might be complex and be a very good estimate, but they are still estimates.

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