Inconsistent SOH vs. Battery Capacity - 90.5% SOH "Stuck" at 250Ah?

[nfcruz]

Hi everyone,


I’m a proud Mach-E ER 2021 owner, but I’m currently scratching my head over some data inconsistencies regarding my battery health. I’m hoping someone here has seen this before and might have some insight.


According to my Car Scanner and FORScan data (attached images), my battery seems to be "capped" by the software:


• Reported SOH: 90.5%


• HVBAT_CAP: Stuck at 250.4 Ah


• The Inconsistency: In my last 100% charge, the car stopped at 82.3 kWh of usable energy (Batt To Empty), but my HVB SOC (Real SOC) was only at 96%.


• Cell Health: My cell voltage variation is perfect (0.006V), and cells reach 4.14V, which proves the hardware is healthy and balanced.


It feels like the BMS is using a very pessimistic SOH/Capacity value to calculate the "Top" of the battery, effectively hiding about 8-9 kWh from me. I’ve already tried a deep calibration cycle (0-100%), but the SOH and Ah values remain frozen.


Has anyone experienced this "software cap"? Is there a way to force the BECM to re-estimate the capacity through FORScan (which is the only tool I currently have access to), or is this a dealer-only fix involving a BECM module reset/update?


I would love to hear your thoughts or if anyone managed to "wake up" the SOH calculation.


Thanks in advance!

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[Shayne]

In my last 100% charge, the car stopped at 82.3 kWh of usable energy

Reported SOH: 90.5%

I think our cars had 88 Kwh to begin and at some point Ford lowered the buffer and raised it to 91 Kwh usable

91 Kwh x 0.905 SOH is 82.355 Kwh. I could be missing something but that calc seems to make sense.

 

[Mach-Lee]

96% actual SoC is as high as it goes because of the top buffer. Everything is normal here.

 

[nfcruz]

I think our cars had 88 Kwh to begin and at some point Ford lowered the buffer and raised it to 91 Kwh usable

91 Kwh x 0.905 SOH is 82.355 Kwh. I could be missing something but that calc seems to make sense.

I see where you're coming from with that calculation, and it does look like it fits at first glance! However, there's a small detail in the math that's still bothering me:


The 82.3 kWh I'm seeing is what I have available at 96% Real SOC (HVB SOC). If my SOH were truly 90.5%, I should only have about 79.4 kWh at that SOC level (\bm{82.3 \text{ predicted total} \times 0.96}).


Since I actually have more energy at 96% than the SOH would predict for a full charge, it feels like the battery is physically healthier than the 90.5% 'label' suggests. It's like having a fuel gauge that says the tank is smaller than it actually is, even though I can clearly see how much fuel is in there!


Just trying to figure out why the BMS is being so conservative with these estimates. Thanks for the brainpower on this! "

 

[nfcruz]

96% actual SoC is as high as it goes because of the top buffer. Everything is normal here.

I totally hear you on the top buffer! Most EVs do keep that safety margin.


However, if 96% HVB SOC is indeed the 'hard ceiling' (100% usable), then the math for 90.5% SOH still hits a snag. If the BMS considers 96% of the raw capacity as the 'new 100%', but I still have 82.3 kWh at that point, the battery is still performing significantly better than a 90% health rating would suggest for a 2021 pack.


Also, my cells are sitting at 4.14V. In most NCM chemistries, there's still a bit of physical room between 4.14V and the typical 4.20V 'raw' peak, which is exactly where that buffer lives.


It just seems my BMS is being extra cautious by reporting a lower SOH than the energy density and voltage actually show. But hey, as long as the car drives this well, I’m happy—just trying to solve the data puzzle! Thanks for the chat!

 

[ipca204]

i'm a novice when it comes to this stuff, but i say don't look a gift horse in the mouth. i would be perfectly happy with a 2021 with that battery....lol

 

[AliRafiee]

This thread is making me dizzy

 

[Mach-Lee]

I totally hear you on the top buffer! Most EVs do keep that safety margin.


However, if 96% HVB SOC is indeed the 'hard ceiling' (100% usable), then the math for 90.5% SOH still hits a snag. If the BMS considers 96% of the raw capacity as the 'new 100%', but I still have 82.3 kWh at that point, the battery is still performing significantly better than a 90% health rating would suggest for a 2021 pack.


Also, my cells are sitting at 4.14V. In most NCM chemistries, there's still a bit of physical room between 4.14V and the typical 4.20V 'raw' peak, which is exactly where that buffer lives.


It just seems my BMS is being extra cautious by reporting a lower SOH than the energy density and voltage actually show. But hey, as long as the car drives this well, I’m happy—just trying to solve the data puzzle! Thanks for the chat!

91 kWh (new) x 90.5% SoH = 82.36 kWh, which is exactly what you saw. Keep in mind the kWh to empty parameter is highly dependent on battery temp. For an accurate comparison, the battery temp must be at 25ºC.

4.14V is the maximum voltage Ford allows you to charge to (100% SoC displayed). Going higher to 4.20V will degrade the pack more, so they've capped it at 4.14V.

Your BMS is functioning normally the same as every other Mach-E.

 

[devmach-e]

SoH determines how much of the battery pack's original capacity is available to you. When new it was 88 or 91 depending upon what year you have for a extended range battery. As the pack ages, you have less capacity. In your case, there's now only ~82 kWh available to you.

The SOC value is in reference to the current capacity of the battery pack. That essentially means instead of 10% capacity representing 8.8 kWh available, it is now representing 8.2 kWh available.

It's like having a 5-gallon jug of water and a 6 gallon jug of water. When each jug of water is full, they are at 100% full. When the 5 gallon jug of water has been half drained there's only 2.5 gallons left. For the 6 gallon jug, 3 gallons are left.

 

[Mache_Nor]

Just to chime in here; I’ve never quite understood how car calculated SoH. My 22 (produced in 21) has always hovered around 89-91.5% SoH depending on season, and my remaining battery capacity is around 85-86 kWh in all my readings. The math doesn’t seem to add up regardless of buffer.

 

[nfcruz]

Bem, analisando seus dados, fica claro que o valor de soh não corresponde a BATT TO EMPTY. Por curiosidade, qual a capacidade em Ah que seu scanner automotivo indica?

 

[NY_Cade69]

I was writing a a way to programmatically calculate and store (for trend analysis), and was trying to validate all of the calculations.
I found that the nominal capacity (not the usable) was not obviously stated.
For the '25 88 kWh it seems that the nominal is 98.8 kWh. Using the 98.8 value in the state of health calculations tracks much better for me.
Open to other's input...

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