Can I trust the displayed battery data?

[dsr]

Apologies for the detail below, but I don’t know how to explain my issue without it.
Wanting to do a full charge to 100% overnight, I set off today on a 45 mile journey. The battery was shown at 23%, with a 53 mile range remaining. On the face of it, the figures seemed weird to me as I expected to get well over 3 miles a kWh. I got home with 3% and 7 miles on the clock. The mileage deduction was pretty exact and I had used 20% of the battery. The ‘problem’ is that the display also showed I had averaged 4.1miles a kWh. If that is correct, I should have something like 12% of the battery left. If the battery reduction and mileage figures are correct, I was getting less than 2.5 miles a kWh.
I guess my bottom line question is whether or not the battery gives less mileage per kWh as it gets closer to 0%? If it maintains a steady miles per kWh, then am I correct in assuming the 23% starting battery figure was wrong and that something closer to 13% would be right?

 

[Koomi]

The GoM is always as the name says, a bit of a guess, and if you are needing to do the 100% balancing charge, it could be out by a bit considering the cold mornings that have not really stopped since November.

But on paper it seems right.
62kWh usable battery @ 4mi/kWh = 248 miles range
which is about 0.4mi per 1%
and therefore 7 miles left is 2.8%

 

[Robf]

I have the same approx 86 mile journey (43 miles each way) every Sunday over the winter, even in low temperatures the car uses 19% there and 21% back (more or less, the trip is a mixture of A roads and motorway, where I keep a steady 65mph if possible). The car has been pretty stable reporting at 3.5 to 4%. Hoping to have much better figures last Sunday at near 20c temp it returned nigh on the same. I would disregard the % efficiency completely and go with the % battery figure..... with a pinch of salt .

 

[MattyS]

a week or so ago I did a journey of 56 miles round trip and started at 50% and got home with 24% which means I was doing around 2.1 miles per %, and used 16.04kwh of battery for an average of 3.49 m/kw.

This was on a very sunny warm day.

I would say there are too many variables to take into account to single out any particular journey and may be a better Idea to track the trend over x times the same journey, because then you are removing some variables.

 

[slmorgan42]

For simple maths year round I just work on 2 miles per 1%. Easy for my old brain.

 

[fnegroni]

The closer you get to 0% the more accurate the GoM is.
The GoM uses the built in factory figures, adjusted by the latest measures SoH, the total accumulated mileage, and the consumption in the last 50miles. In different proportions. This is known as weighting.
The weighting of each figure is then used to predict the mileage left based on the predicted charge left in the battery.
This is also assuming the battery pack is balanced and the voltage at lower states of charge is known to a reasonable level of accuracy.
This is also then adjusted by taking into account whether the HVAC is on or off, the driving mode, the battery temperature, and the ambient temperature.

Finally, the weighting is such that at higher states of charge it seems optimistic but also doesn’t cause range anxiety, then below 50% starts to be way more accurate and if you have been driving over a long distance it’s pretty spot on.

What most EV drivers do however is forgetting that the higher the efficiency figures, the higher the impact of each and every unnecessary acceleration and braking.

 

[EvTek23]

I travel reasonably regular trips to Dorset from Bucks,100 miles each way, and find that although the route is the same there and back I get a large variation of both the % of battery used and the energy consumed. For example on my latest journey:
34% of battery, 20kWh energy, 4.8mls/kWh, 11 degrees temp.
return:
49% of battery, 28kWh energy, 3.4mls/kWh, 4 degrees temp.
I've noted consistently over previous journeys that the return consumes far more power. I travel at the same speed, around 60 mph on the motorways and A roads. So apart from from changes in the terrain the only other variable is the air temperature, is it really 8kWh to heat the car for two and a half hours with an outside temperature difference of 7 degrees?

 

[EvTek23]

Looking at comment from @fnegroni perhaps the biggest variable with the GOM accuracy might be, that normally on my outward journey I charge to 100%, (so if for any reason I have to make the return journey without charging I have enough left) but for my return only charge to 80%. It still doesn't account for the actual energy consumption, (20kWh verses 28kWh), typically 35% battery on the outward journey and 50% battery on the return.

 

[fnegroni]

The routes are the inverse of each other.
What’s the total elevation gain/loss on the way there? What are they on the return journey?
What’s the total time and average speed?
What direction and speed is the wind blowing?
P.S. When the battery is cold in the morning, and charged to 100% your regen is severely limited.

What you need to compare is like for like: if all your outbound journeys have similar consumption, then there’s your answer.

 

[EvTek23]

@fnegroni
The routes are the invers of each other, 101.4 mls outgoing, 101.3 return.
Elevation difference is about 450 feet lower at the destination compared to the start, (450 feet higher on the return) but there are many gradients on the way rather than the total elevation change.
Total time of each journey 2:35 outgoing, 2:22 return.
Average speed 40 outgoing, 42 return.
Wind direction and speed could therefore be another factor.

 

[fnegroni]

@fnegroni
The routes are the invers of each other, 101.4 mls outgoing, 101.3 return.
Elevation difference is about 450 feet lower at the destination compared to the start, (450 feet higher on the return) but there are many gradients on the way rather than the total elevation change.
Total time of each journey 2:35 outgoing, 2:22 return.
Average speed 40 outgoing, 42 return.
Wind direction and speed could therefore be another factor.

so your journey on the way out is more downhill than uphill but you start with a 100% battery, possibly too cold anyway for maximum regen, which means you are possibly missing out on a trick here whereby charging only to 80% before your outward journey.

Also are the climbs/descents steeper on the way out or back?

Btw, I did ask about the total elevation gained/lost:

Total elevation gain refers to the cumulative amount of vertical ascent achieved during an activity. It measures how much you climb overall, regardless of any downhill sections in between.

For example, if you hike up a hill that’s 100 meters high, descend to the base, and then climb another 150-meter hill, your total elevation gain would be 250 meters, even though your starting and ending elevation might be the same.

If you could brake it down into three sections then you would have the idea of which section requires a warmer and less charged battery to be the most efficient in regen.

Honestly though we are trying to split hairs. As I mentioned in my earlier post, EV drivers tend to forget that the higher the efficiency , the more the impact of every single acceleration and braking.

If you think of your baseline consumption, as long as you don’t deep below that, everything above it is a plus. Ultimately you could try and hypermile your commute in which case if I were you I would invest in an aerodynamics book (my son and I are actually studying that) to improve it much further through some clever trickery.

 

[Anon70]

You could also check the status of all of the trip functions as the accumulated totals will auto reset after 999 miles if you do not manually reset it and these will show different efficiency figures.

 

[EvTek23]

@fnegroni you make a very valid point about the total elevation gain. It is something that I'd considered might well make a difference due to the consistency of the outgoing journey and return variations.
I have installed a GPS geotracker so that I can capture the total elevation gain over my next journey to Dorset

 

[Rolfe]

I regularly go to Glasgow and back. I live at about 800 feet, and Glasgow is at sea level. Invariably I use more on the homeward journey than the outward.

Other factors are that I'm usually going home in the late evening when it's colder, and at a time when it's possible to drive faster than earlier in the day when there's more traffic around.

 

[GoElectric]

From my thousands of kilometers driven on my commuting route, all the numbers here are within average of what I get. So, your cars are OK. 19% at 68 mph for a 43 mile leg is normal when accounting for hills etc. If it were always completely flat and warm, 19% @ 68 mph could probably do 55 miles. I've come to completely trust the GOM. It's good enough. Though, I wish the average consumption would update more frequently.

64kWh model has a realistic range of 215 mi on a single charge at leisurely highway speeds.