Does the dash charge level gauge lie?

[933233311602]

The dash fuel gauges in ICE cars lie when the gas tank is full. They won't show a dip from "full" until well after the tank is less than full. I think most people know this from over the decades. Drivers hate seeing their "full tank" level drop so the gauges are intentionally made to lie. (Likewise, "empty" isn't actually empty and customers expect to still have some "fumes" driving left even when the gauge says "empty")

I've noticed that when I charge to 100%, the gauge stays at 100% for a suspiciously longer time than driving with less charge.

Does anyone know if the charge gauge also lies like an ICE car fuel gauge?

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[Dustus]

That is odd. My car drops at least a 1 percent just backing out of my driveway. I think mine is tuned backwards.

 

[Maquis]

I almost never charge to 100% (normally 85), but I’ve seen a few times after charging that I can go more miles before it drops a % than it should. One time, almost 10 miles before it decremented. I don’t really worry about it.

ETA…temperature plays a role here. If you charge to X%, then later the temperature goes up, so will the SoC. But the car will never report more than 100.

 

[Maquis]

That is odd. My car drops at least a 1 percent just backing out of my driveway. I think mine is tuned backwards.

I’ve had that happen, too.

 

[ReverendPete]

It seems like most of the electric cars do have a little reserve after they hit zero, much like the old old ICE cars that had a little lever to swap to a "reserve tank" when you ran out of gas. According to MoveElectric, their experience with MME was this:

"Once 0% was displayed, the car managed a whole loop of the 15-mile test circuit at varying speeds but when it was about to go for another run the car was unresponsive. Power steering was unoperational, although some systems remained."

https://www.moveelectric.com/e-cars/what-happens-when-electric-car-runs-out-battery

 

[JohnFoxeSheets]

The dash fuel gauges in ICE cars lie when the gas tank is full. They won't show a dip from "full" until well after the tank is less than full. I think most people know this from over the decades. Drivers hate seeing their "full tank" level drop so the gauges are intentionally made to lie. (Likewise, "empty" isn't actually empty and customers expect to still have some "fumes" driving left even when the gauge says "empty")

I've noticed that when I charge to 100%, the gauge stays at 100% for a suspiciously longer time than driving with less charge.

Does anyone know if the charge gauge also lies like an ICE car fuel gauge?

Measuring battery state of charge (SoC) is an inexact science. Additionally the SoC is impacted by temperature, so what appears as 100% will be different depending on a range of factors. I wouldn’t call it lying - I would simply say that the charge meter does as best as it can. But it is true that it will never show more than 100%, even if conditions change.

Where are you located? If you have large temperature swings, that might explain what you’re seeing.

 

[kdonnel]

My normal charge limit is 85%. I am at 84% before I hit the end of the street because I feel like it stops the charge at 84.9999999%.

When I charge to 100% for a trip I fee like it charges to 100.99999999% and I end up a few miles down the street before it drops to 99%.

 

[AKgrampy]

I can tell you that I have left a heated garage with 90% SOC and driven at -30F for 10 miles and arrived at my destination with a 94% SOC.

 

[JohnFoxeSheets]

I can tell you that I have left a heated garage with 90% SOC and driven at -30F for 10 miles and arrived at my destination with a 94% SOC.

This makes perfect sense. The displayed SoC is temperature dependent. A warm battery can hold more energy than a cold one. But since it would be too confusing for a cold battery to not be able to be charged to 100%, Ford (and I suspect most other manufacturers) display the SoC is a function of the battery capacity in its current conditions, including temperature.

When the battery is nestled up tight in your warm garage more electrons can go into the battery than when it is cold. So your 90% SoC become 94% SoC as the battery cools, even though you're driving. Had you just taken the car out of the garage and left it for a few hours, the SoC would have gone up even more.

This is why I suspect that the OP lives in an area with large night to day temperature swings...

 

[thenew3]

The % is based on battery voltage. Similar to phones, computers and anything else that uses batteries, the drop from 100% to 99% is slow compared to drop from 99% to 98%.

I noticed when I charge the MME to 100% it takes a good 10-15 miles before it drops to 99%, however when I charge it to 90%, it drops down to 89% as soon as I unplug the charger and start the car and then quickly drops to 88% within 1-2 miles. When I charge it to 80%, it takes a good 5-10 miles to drop down to 79%. (all tested on the same roads)

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