Battery went from 7% to 0 and left me stranded 6 miles from charger.

[Yellow Buddy]

Honestly at this point if you want to extend range, I think that you need to follow the battery voltage which you can only see with an OBDII scanner.

Which truly defeat the purpose. In the majority of cases, it doesn't make sense to sit there at 64kW. If it's available, you're better off hopping to the next charger and grabbing 167kW.

I've got an OBDII that I've used on a couple of road trips but realistically not many people are going to be pulling up their OBD mid drive to look at voltages, then do calculations, then pull up Tesla/Plugshare/EA to figure out where the next stop should be.

Maybe a couple of us nerds, but the majority would likely be stranded on the side of the road researching how much the Lightning is worth and how much it would cost for a F-150 EcoBoost Hybrid or a Silverado with the big battery.

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[Newton]

I agree, it is a problem. Fortunately most people don't try to drive to that low of a battery percentage. However, Ford should not count it as range when they sell the truck if it can't achieve it, 'battery at 5%' is no good if the truck doesn't move.

My EV6 does not seem to have this problem.

 

[Newton]

It is the problem with dumbing down the UI. If we had a proper technical screen with voltage, amps remaining (estimated) and a graph of miles/kWh we could be telling people "don't drive the truck below X voltage" (or whatever) and they could adapt. Instead all that is shown is an inaccurate guess-o-meter and an inaccurate battery percentage guess. Nobody knows how they work (probably not many at Ford even) so it is hard to predict and leads to anxiety.

I had this fight all the time as a developer and always lost. We don't want somebody's mom to be scared by a detailed error message, so we just bomb out with a "Sorry, something went wrong." The opposition forgets that people can google a detailed error message, where as "something went wrong" is no help at all.

 

[ctuan13]

Okay. Strangely a very similar thing just happened to me TODAY driving home from work (work is 200 miles from home). Exited the freeway and slowed to a stop with 6%soc and at about 85% power. Suddenly while sitting at the light the power meter began dropping 80-65-40-15-13-2 pressing the accelerator did nothing. Threw on the hazards, shut the truck off and back on. Back to 85% power I drive thru the intersection and it again tapers back to 2% power and I lose all throttle response. Get it towed 1 mile home. Plug it in and now there seems to be no issue. I’ve taken the truck to 8-10% soc several times over the past two years without issue. Guess anything less than 5% soc is a no go

Oh wow, so it's not just OP who's had this issue.

Now I'm curious and maybe @MickeyAO can chime in here to tell me whether I'm on the right track or totally off base, but I wonder if it has something to do with never charging to 100% for a true top balance. In theory, this could lead to a deviating BMS state of charge reading whose accuracy or lack thereof will be most pronounced at the extreme top or bottom of the battery state of charge.

How often do you charge to 100%?

 

[MickeyAO]

Oh wow, so it's not just OP who's had this issue.

Now I'm curious and maybe @MickeyAO can chime in here to tell me whether I'm on the right track or totally off base, but I wonder if it has something to do with never charging to 100% for a true top balance. In theory, this could lead to a deviating BMS state of charge reading whose accuracy or lack thereof will be most pronounced at the extreme top or bottom of the battery state of charge.

How often do you charge to 100%?

I cannot not tell you how specifically the BMS works or if 100% will help...I'm a cell expert and can tell you how to make them live almost forever. I will say that usually, the SOC is based on voltage only.

If you do find yourself stuck and unable to move forward, try driving in reverse

 

[ctuan13]

I cannot not tell you how specifically the BMS works or if 100% will help...I'm a cell expert and can tell you how to make them live almost forever. I will say that usually, the SOC is based on voltage only.

If you do find yourself stuck and unable to move forward, try driving in reverse

Ahh I see, interesting! I'd imagine though on NMC batteries, the voltage curve, though more sloped than LiFePO4, is still pretty flat, so it'd have to be very sensitive electronics to detect those changes. I would've figured they'd also use some sort of columbmeter reading, maybe in conjunction with voltage. I know you're mainly a cell expert, but does that sound at all accurate to you?

 

[Yellow Buddy]

Oh wow, so it's not just OP who's had this issue.

Now I'm curious and maybe @MickeyAO can chime in here to tell me whether I'm on the right track or totally off base, but I wonder if it has something to do with never charging to 100% for a true top balance. In theory, this could lead to a deviating BMS state of charge reading whose accuracy or lack thereof will be most pronounced at the extreme top or bottom of the battery state of charge.

How often do you charge to 100%?

Charging to 100% and top balancing doesn’t help. My truck sees 100% quite frequently and I still ran out.

 

[MickeyAO]

Ahh I see, interesting! I'd imagine though on NMC batteries, the voltage curve, though more sloped than LiFePO4, is still pretty flat, so it'd have to be very sensitive electronics to detect those changes. I would've figured they'd also use some sort of columbmeter reading, maybe in conjunction with voltage. I know you're mainly a cell expert, but does that sound at all accurate to you?

No. While I use coulomb counting in my cell testing, it does not do well in strings.

 

[ctuan13]

No. While I use coulomb counting in my cell testing, it does not do well in strings.

Wow, okay very interesting. See this is why I love having guys like you on the forum where we can pick your brain! My only experience with lithium batteries and BMSs is either repairing small electronics or building management systems with LiFePO4 batteries for RV or off grid applications. Thanks for the insight, man!

 

[Grumpy2]

I have been working my way thru Dr.Dahn writings:
https://scholar.google.com/citation...&user=upVeFJoAAAAJ&pagesize=80&sortby=pubdate
If only there was a published chart with cell voltage value after polarization when the dash says 100%.

 

[Newton]

No. While I use coulomb counting in my cell testing, it does not do well in strings.

I think am beginning to understand why many EV manufacturers pretty much hide (or completely omit) any sort of battery percentage from their MMI. I find it unfortunate that Fords 'public' battery percent is more optimistic than the internal one, because it is apparently not reset lower when the internal counter is adjusted for resting voltage or even after a drive!

On one day during a road trip, I charged to 100%. I took measurements while we were packing the truck immediately after unplugging at various times because as usual I kept thinking that we were about to go and there was one more thing to do. The final reading was after a short drive.

Time	Internal SOC	Public SOC	Internal kWh
6:21 AM	98.85	100	94.72
6:23 AM	95.73	100	94.56
6:33 AM	95.17	100	93.85
6:54 AM	93.04	100	91.48

The whole time, my dash said "100%". So to the truck, '100%' means anything from 94.72 kWh to 91.48 kWh. The internal state of charge dropped 5%! Thats a 7.5 mile difference at my 2.3 mi/kWh average on that trip.

I can understand Ford's dilemma - if they told the truth my full charge would be only 99% and it would drop to 95% doing nothing for half an hour. Customers would not like that. However it appears that the truck bases some behaviors on the totally bogus Public SOC, such as when to reduce DC fast charging to 40kW - it is always at exactly 80% on my dash. I wonder how they do the power reduction, off of voltage or again off of a bogus BMS reading?


Tesla and Kia seem to have it figured out, perhaps they just include a much bigger buffer at the bottom (and they are starting with much more efficient cars.)

 

[Newton]

I found the graph data for this time period. The graph line for the "public" state of charge (SOCD) was always 100. I discovered that the last data point was after a short drive which makes the displayed state of charge even weirder, since it remained at 100%

 

[lightspeed]

If you use an ODBII scanner you will find that there are two state of charges - the one that is displayed and an internal state. They almost never agree and rarely show the appropriate percentage for the battery size. At higher states of charge the internal state is always *less* than the displayed state (by up to 7%), at lower it reverses although they are then closer.

The displayed state really drifts around, to the point that I consider it useless. The internal state will be higher immediately after a charge and will drop down over 20 minutes as reported.

The nasty trick to all of this is that when you charge the truck, it uses the displayed state to control - so when the displayed state hits 80% you drop down to 40kW. However, at that point the truck really thinks that the battery is at 72%. The power limitations seem to be software controlled, but I do not have enough data to know which of the two states of charge are used for that.

Honestly at this point if you want to extend range, I think that you need to follow the battery voltage which you can only see with an OBDII scanner.

This is by design. FORD reserves around 9% of the battery for longevity.

So, 131kWh is going to read 100% to users even though it's only 91% of the full 143kWh battery.

 

[Newton]

This is by design. FORD reserves around 9% of the battery for longevity.

So, 131kWh is going to read 100% to users even though it's only 91% of the full 143kWh battery.

That assumption is not supported by the data that I have for my truck. If this were the case

• The internal "kWh to empty" divided by the internal "SOC" percentage should yield the actual battery size, in your case 143kWh (I have a SR). It does not.
• This value should remain relatively constant as the state of charge varies. It does not.
• The internal state of charge should always be smaller than the public value. It is not, at low state of charge it is actually *larger*.
• If the public "SOC Displayed" is 6% the truck should not run out of energy, as the OP experienced.

 

[lightspeed]

That assumption is not supported by the data that I have for my truck. If this were the case

• The internal "kWh to empty" divided by the internal "SOC" percentage should yield the actual battery size, in your case 143kWh (I have a SR). It does not.
• This value should remain relatively constant as the state of charge varies. It does not.
• The internal state of charge should always be smaller than the public value. It is not, at low state of charge it is actually *larger*.
• If the public "SOC Displayed" is 6% the truck should not run out of energy, as the OP experienced.

The public SoC is heading from 100% to 0% once 131kWh (of the 143kwH) have been consumed.

FORD doesn't tell us what the reserves are, but based on 96% internal when public SoC is 100%, in an ER, it looks like they reserve about 6kWh at the top and 6kWh at the bottom. This let's us use 131kWh out of the total 143kWh.

So at 0% public SoC, the internal charge is still 4% (the reserve).

Therefore, there is a crossover point where the internal SoC will be greater than the public SoC and this happens around 50% of public SoC.

Here's a graph to help make it visual:

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